iwlwifi: mvm: add beamformer support

VHT Beamformer (BFER) will be used if the peer supports it
and there's a benefit to use it vs. STBC or SISO.
The driver now tells the FW whether BFER and/or STBC are
allowed but the FW will make the decision to use either
or stick to SISO on its own.
BFER is limited to a single remote peer. The driver takes
care of ensuring this to the FW and prioritizes with which
peer BFER will be used.

Signed-off-by: Eyal Shapira <eyalx.shapira@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>