Bluetooth: controller: radio: Add back2back TX switch after PHYEND event

Transmission of Constant Tone Extension is done after END event
triggered by radio. To correctly switch from TX to TX (back 2 back
TX) after transmission of CTE PHYEND event must be used instead of
END event.

The commit provides required function that allows LLL to correctly
setup radio to do back to back switch of TX when CTE transmission
is enabled.

The radio_switch_complete_and_phy_end_b2b_tx cannot be implemented
in radio.c source file. It will fail build of unit tests targeted
for NRFBSIM simulator board. There is no RADIO_SHORTS_PHYEND_DISABLE_Msk
macro defined in bsim_hw_models module.

Signed-off-by: Piotr Pryga <piotr.pryga@nordicsemi.no>