Bluetooth: controller: PHY Update Procedure

Added support for Bluetooth v5.0 PHY Update Procedure in the
Controller.

Asymmetric PHY connections do not work for now due to the
Radio mode not being setup in time in the ISR during tIFS
period and the Radio already ramping up in the cached
previous Radio mode to meet tIFS deadline.

Subsequent commits will add this feature, by either double
buffering the mode in software or using fast radio ramp up
which gives enough time in the ISR to change the mode.

Jira: ZEP-2086

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