Bluetooth: Controller: Explicitly set all bits of used radio registers

Explicitly set all bits of used radio registers when
configuring radio events, removing the dependency on having
the power-on reset value and removing the need to ensuring
power-on reset values being set in the radio peripheral.

This will ensure the Controller has radio register value
correctly configured irrespective of changes across SoCs'
radio register power-on reset values.

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