NRF5x: Increase lp us ticker interrupt priority

Set the second highest user level, leaving the highest for UART (we are having constant overflows) and two levels below for everything else.
This should increase the timer accuracy.

Author: mprse

targets/TARGET_NORDIC/TARGET_NRF5x/common_rtc.c

@@ -173,13 +173,7 @@ void common_rtc_init(void)
     nrf_rtc_int_disable(COMMON_RTC_INSTANCE, LP_TICKER_INT_MASK);
 #endif
 
-    nrf_drv_common_irq_enable(nrf_drv_get_IRQn(COMMON_RTC_INSTANCE),
-#ifdef NRF51
-        APP_IRQ_PRIORITY_LOW
-#elif defined(NRF52) || defined(NRF52840_XXAA)
-        APP_IRQ_PRIORITY_LOWEST
-#endif
-        );
+    nrf_drv_common_irq_enable(nrf_drv_get_IRQn(COMMON_RTC_INSTANCE), APP_IRQ_PRIORITY_HIGH);
 
     nrf_rtc_task_trigger(COMMON_RTC_INSTANCE, NRF_RTC_TASK_START);
 

targets/TARGET_NORDIC/TARGET_NRF5x/us_ticker.c

@@ -89,14 +89,7 @@ void us_ticker_init(void)
 
     NVIC_SetVector(TIMER1_IRQn, (uint32_t)us_ticker_irq_handler);
 
-    nrf_drv_common_irq_enable(TIMER1_IRQn,
-
-#ifdef NRF51
-        APP_IRQ_PRIORITY_LOW
-#elif defined(NRF52) || defined(NRF52840_XXAA)
-        APP_IRQ_PRIORITY_LOWEST
-#endif
-        );
+    nrf_drv_common_irq_enable(TIMER1_IRQn, APP_IRQ_PRIORITY_HIGH);
 
     nrf_timer_task_trigger(NRF_TIMER1, NRF_TIMER_TASK_START);