iwlwifi: move ht40 bitmap into config

iwlwifi: move ht40 bitmap into config

There's no need to dynamically fill the HT40
band bitmap as it's a device parameter, just
put it into the HT configuration.

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