bluetooth: controller: nrf5: Refactor a bit radio_nrf5_ppi.h

Change hard-coded (D)PPI channel bitfield values to the BIT() macro
calls with the corresponding channel base value supplied as parameter,
to make it possible to actually change this base value if needed.
Remove unused *_EXCLUDE macros.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>