iwlwifi: move RF config into NIC config

Since the RF config is done for all devices,
there's no need to keep a separate function
that is called for all devices, move it into
the general NIC config function.

Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Reviewed-by: Wey-Yi W Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>