drm/radeon: add DisplayPort MST support (v2)

This adds initial DP 1.2 MST support to radeon, on CAYMAN
and up in theory.

This is off by default.

v2: agd5f:
- add UNIPHY3 offsets
- move atom cmd table code into atombios_encoders.c
- whitespace cleanup
- replace some magic numbers with proper defines

Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_atombios.c

@@ -845,6 +845,7 @@ bool radeon_get_atom_connector_info_from_object_table(struct drm_device *dev)
 
 	radeon_link_encoder_connector(dev);
 
+	radeon_setup_mst_connector(dev);
 	return true;
 }