RAT (Radio Timer) handling for CC13xx/CC26xx

Files
file	arch/cpu/simplelink-cc13xx-cc26xx/rf/rat.c
	Implementation of the CC13xx/CC26xx RAT (Radio Timer) upkeep.
file	arch/cpu/simplelink-cc13xx-cc26xx/rf/rat.h
	Header file of the CC13xx/CC26xx RAT timer handler.

Detailed Description