[EFM32] Add delay after reset for greentea test runs.

The host-test resets the target by sending a UART break. After this, it takes some
time for the target to come back up. Without this timeout, the __sync packet
sent by greentea would not be retransmitted by the interface chip (i.e. it would never
reach the target). Testing on different devices indicates that 2 seconds delay
is sufficient for the device to reset and the  __sync packet to reach the target.

Author: asmellby

hal/targets.json

@@ -1554,7 +1554,8 @@
         "extra_labels": ["Silicon_Labs", "EFM32"],
         "supported_toolchains": ["GCC_ARM", "ARM", "uARM"],
         "progen": {"target": "efm32gg-stk"},
-        "device_has": ["ANALOGIN", "ANALOGOUT", "ERROR_PATTERN", "I2C", "I2CSLAVE", "I2C_ASYNCH", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_ASYNCH", "SLEEP", "SPI", "SPISLAVE", "SPI_ASYNCH", "STDIO_MESSAGES"]
+        "device_has": ["ANALOGIN", "ANALOGOUT", "ERROR_PATTERN", "I2C", "I2CSLAVE", "I2C_ASYNCH", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_ASYNCH", "SLEEP", "SPI", "SPISLAVE", "SPI_ASYNCH", "STDIO_MESSAGES"],
+        "forced_reset_timeout": 2
     },
     "EFM32LG_STK3600": {
         "inherits": ["Target"],
@@ -1563,7 +1564,8 @@
         "extra_labels": ["Silicon_Labs", "EFM32"],
         "supported_toolchains": ["GCC_ARM", "ARM", "uARM"],
         "progen": {"target": "efm32lg-stk"},
-        "device_has": ["ANALOGIN", "ANALOGOUT", "ERROR_PATTERN", "I2C", "I2CSLAVE", "I2C_ASYNCH", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_ASYNCH", "SLEEP", "SPI", "SPISLAVE", "SPI_ASYNCH", "STDIO_MESSAGES"]
+        "device_has": ["ANALOGIN", "ANALOGOUT", "ERROR_PATTERN", "I2C", "I2CSLAVE", "I2C_ASYNCH", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_ASYNCH", "SLEEP", "SPI", "SPISLAVE", "SPI_ASYNCH", "STDIO_MESSAGES"],
+        "forced_reset_timeout": 2
     },
     "EFM32WG_STK3800": {
         "inherits": ["Target"],
@@ -1572,7 +1574,8 @@
         "extra_labels": ["Silicon_Labs", "EFM32"],
         "supported_toolchains": ["GCC_ARM", "ARM", "uARM"],
         "progen": {"target": "efm32wg-stk"},
-        "device_has": ["ANALOGIN", "ANALOGOUT", "ERROR_PATTERN", "I2C", "I2CSLAVE", "I2C_ASYNCH", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_ASYNCH", "SLEEP", "SPI", "SPISLAVE", "SPI_ASYNCH", "STDIO_MESSAGES"]
+        "device_has": ["ANALOGIN", "ANALOGOUT", "ERROR_PATTERN", "I2C", "I2CSLAVE", "I2C_ASYNCH", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_ASYNCH", "SLEEP", "SPI", "SPISLAVE", "SPI_ASYNCH", "STDIO_MESSAGES"],
+        "forced_reset_timeout": 2
     },
     "EFM32ZG_STK3200": {
         "inherits": ["Target"],
@@ -1585,7 +1588,8 @@
             "target": "efm32zg-stk"
         },
         "device_has": ["ANALOGIN", "ERROR_PATTERN", "I2C", "I2CSLAVE", "I2C_ASYNCH", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_ASYNCH", "SLEEP", "SPI", "SPISLAVE", "SPI_ASYNCH", "STDIO_MESSAGES"],
-        "default_build": "small"
+        "default_build": "small",
+        "forced_reset_timeout": 2
     },
     "EFM32HG_STK3400": {
         "inherits": ["Target"],
@@ -1598,7 +1602,8 @@
             "target": "efm32hg-stk"
         },
         "device_has": ["ANALOGIN", "ERROR_PATTERN", "I2C", "I2CSLAVE", "I2C_ASYNCH", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_ASYNCH", "SLEEP", "SPI", "SPISLAVE", "SPI_ASYNCH", "STDIO_MESSAGES"],
-        "default_build": "small"
+        "default_build": "small",
+        "forced_reset_timeout": 2
     },
     "EFM32PG_STK3401": {
         "inherits": ["Target"],
@@ -1607,7 +1612,8 @@
         "extra_labels": ["Silicon_Labs", "EFM32"],
         "supported_toolchains": ["GCC_ARM", "ARM", "uARM", "IAR"],
         "progen": {"target": "efm32pg-stk"},
-        "device_has": ["ANALOGIN", "ERROR_PATTERN", "I2C", "I2CSLAVE", "I2C_ASYNCH", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_ASYNCH", "SLEEP", "SPI", "SPISLAVE", "SPI_ASYNCH", "STDIO_MESSAGES"]
+        "device_has": ["ANALOGIN", "ERROR_PATTERN", "I2C", "I2CSLAVE", "I2C_ASYNCH", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_ASYNCH", "SLEEP", "SPI", "SPISLAVE", "SPI_ASYNCH", "STDIO_MESSAGES"],
+        "forced_reset_timeout": 2
     },
     "WIZWIKI_W7500": {
         "supported_form_factors": ["ARDUINO"],