iwlwifi: mvm: Change FW channel info API

Change iwl_fw_channel_info structure so it can have channel number
greater than 255. This is needed for 6 GHz channel numbers.
Change all relevant structs and member accesses accordingly.
The new API is indicated by a TLV capability bit.

Signed-off-by: David Spinadel <david.spinadel@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>