iwlwifi: pcie: switch to correct RBD/CD layout for 22560

The layout of the RBD (receive buffer descriptor) isn't quite right,
the hardware ended up being implemented differently. Switch to the
correct RBD layout. While at it, remove the now useless extra defines.

Also, switch the CD (completion descriptor) to the right format, which
is basically just a code cleanup because the only field we really used
(rbid) is still in the same place. We may need fragmentation later if
we ever want to use it.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>