drm/i915: Use uabi engines for the default engine map

Default engine map is exactly about uabi engines so no excuse not to use
the appropriate iterator to populate it.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
[tursulin: Fixed up r-b tag spelling.]
Link: https://patchwork.freedesktop.org/patch/msgid/20230123185629.1593320-1-jonathan.cavitt@intel.com