Fix compatibility with Silicon Labs boards

The Silicon Labs core moved to use ArduinoCore-API which
has a native 'BitOrder' definition

Author: silabs-bozont

Adafruit_SPIDevice.h

@@ -23,7 +23,7 @@ typedef uint8_t SPIClass;
     defined(ARDUINO_AVR_ATmega3208) || defined(ARDUINO_AVR_ATmega1609) ||      \
     defined(ARDUINO_AVR_ATmega1608) || defined(ARDUINO_AVR_ATmega809) ||       \
     defined(ARDUINO_AVR_ATmega808) || defined(ARDUINO_ARCH_ARC32) ||           \
-    defined(ARDUINO_ARCH_XMC) || defined(ARDUINO_SILABS)
+    defined(ARDUINO_ARCH_XMC)
 
 typedef enum _BitOrder {
   SPI_BITORDER_MSBFIRST = MSBFIRST,