This PR provides implementation of ticker_free() function for the following boards:
ARCH_PRO
EV_COG_AD3029LZ
EV_COG_AD4050LZ
K22F
K64F
K82F
KW24D
KW41Z
LPC546XX
NRF51_DK
NRF52_DK
NUCLEO_F207ZG
NUCLEO_F401RE
NUCLEO_F429ZI
NUCLEO_F746ZG
REALTEK_RTL8195AM
The unified NRF51 target and feature BLE directories have been
reorganized to follow the naming and directory structure of the
NRF52 implementation.
This reorganization does not include TARGET_MCU_NRF51822 and
derived targets.