Bluetooth: controller: Introduce s/w based TRX switching

Introduce alternative TRX switching using dedicated timers
and peripheral interconnect. This will enable the
possibility to independently configure the Tx and Rx
settings between the tIFS.

Note, this will also provide the opportunity to design a
soft realtime Radio ISR.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>