drm/amd/display: Alpha plane type

Add Alpha surface type for future use
Signed-off-by: Eric Bernstein <eric.bernstein@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hubp.h

@@ -459,6 +459,7 @@
 	type ROTATION_ANGLE;\
 	type H_MIRROR_EN;\
 	type SURFACE_PIXEL_FORMAT;\
+	type ALPHA_PLANE_EN;\
 	type SURFACE_FLIP_TYPE;\
 	type SURFACE_FLIP_MODE_FOR_STEREOSYNC;\
 	type SURFACE_FLIP_IN_STEREOSYNC;\