iwlwifi: implement dynamic opmode loading

This is the next step in splitting up the driver,
making the uCode API dependent pieces of it live
in separate modules. Right now there's only one
so it's not user-selectable, but we're actively
working on more.

Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Don Fry <donald.h.fry@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>