Now that we have two drivers (DVM and MVM) stop selecting
the DVM one (but make it default) and allow enabling only
the MVM driver if so desired. Add a warning for the case
of having neither DVM nor MVM enabled -- that's useless.
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>