Bluetooth: Controller: nRF54Lx: Use nrfx interface for bsim use (1/4)

Use nrfx interface for register access with sideeffects to
facilitate bsim use.

4 part commits:
1. Add nrf_grtc interface.
2. Remove CMSIS interface use.
3. Add nrf_grtc interface, once missing bsim port available.
4. Remove CMSIS interface use, replaced by bsim port.

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