Add easy to remember alias for LL_RCC_ForceCM4Boot

Author: sebromero

cores/arduino/Arduino.h

@@ -74,6 +74,7 @@ extern "C"{
 
 #define interrupts()        __enable_irq()
 #define noInterrupts()      __disable_irq()
+#define bootM4() LL_RCC_ForceCM4Boot()
 
 // We provide analogReadResolution and analogWriteResolution APIs
 void analogReadResolution(int bits);