Bluetooth controller nrf: nrf52 bsim radio hal header minor updates

Align the header a bit with the one for the real radio,
adding missing Tx power levels and removing TODO which did not
need doing.
The old one originated as a copy of the nrf52833 one, and did not
evolve like the real ones.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>