Changed ARM_PMU_Get_EVCNTR() function to mask top 16 bits of result so it's...

Changed ARM_PMU_Get_EVCNTR() function to mask top 16 bits of result so it's guaranteed to work across any Armv8.1-M implementation (not just Cortex-M55)
Fixed macro four definitions in core_cm55.h and core_armv81mml.h:
- PMU_EVCNTR_CNT_Msk
- PMU_EVTYPER_EVENTTOCNT_Msk
- PMU_TYPE_NUM_CNTS_Msk
- PMU_TYPE_SIZE_CNTS_Msk
Added macro definitions for the PMU Authentication Status Register.
Changed the dates at the top of each file.