Bluetooth: controller: LLL: Fix not switching antennas in AoD mode

Antenna switching done by Radio with use of GPIOs provided in
PSEL.DFEGPIO registers. Registers were initialized once during
controller initialization.
At preparation of new radio event, Radio peripheral is powered
down and up to resset its registers. It is related with multi
protocol handling and possible leftovers in Radio registers.

Due to that, PSEL.DFEGPIO registers should be initialized
at the preparation of every event that will transmit
or receive CTE and run antenna switching.

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