Bluetooth: controller: Add DF initialization to controller init sequence

Direction Finding requires initalization of a set of registers
in Radio peripheral. Also it requires information about antenna
matrix unit that are provided by end user in DTS overlay.
Implemented initialization step is responsible for validation of
hardware information delivered by DTS and setting up DF related
registers in Radio.

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