iwlwifi: mvm: advertise VHT capabilities

Update the NVM parsing functions to add VHT capabilities;
they are only added for 5 GHz, of course. This assumes
that all devices with NVM reading (rather than EEPROM)
that support 5 GHz have VHT, which is true right now.

Signed-off-by: Eytan Lifshitz <eytan.lifshitz@intel.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>