Bluetooth: controller: radio: add fun to switch to RX after PHYEND evt

When PDU has CTE added to the end, the PHYEND event must be used
to correclty switch between TX and RX. END event is triggered just
before start of CTE.
The commit adds new function that configures radio to disable after
PHYEND is generated and then swtich to RX.

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