drm/object: Add default color encoding and range value at reset

The drm_plane_create_color_properties() function asks for an initial
value for the color encoding and range, and will set the associated
plane state variable with that value if a state is present.

However, that function is usually called at a time where there's no
state yet. Since the drm_plane_state reset helper doesn't take care of
reading that value when it's called, it means that in most cases the
initial value will be 0 (so DRM_COLOR_YCBCR_BT601 and
DRM_COLOR_YCBCR_LIMITED_RANGE, respectively), or the drivers will have
to work around it.

Let's add some code in __drm_atomic_helper_plane_state_reset() to get
the initial encoding and range value if the property has been attached
in order to fix this.
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220221095918.18763-19-maxime@cerno.tech

drivers/gpu/drm/drm_atomic_state_helper.c

@@ -251,6 +251,20 @@ void __drm_atomic_helper_plane_state_reset(struct drm_plane_state *plane_state,
 	plane_state->alpha = DRM_BLEND_ALPHA_OPAQUE;
 	plane_state->pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;
 
+	if (plane->color_encoding_property) {
+		if (!drm_object_property_get_default_value(&plane->base,
+							   plane->color_encoding_property,
+							   &val))
+			plane_state->color_encoding = val;
+	}
+
+	if (plane->color_range_property) {
+		if (!drm_object_property_get_default_value(&plane->base,
+							   plane->color_range_property,
+							   &val))
+			plane_state->color_range = val;
+	}
+
 	if (plane->zpos_property) {
 		if (!drm_object_property_get_default_value(&plane->base,
 							   plane->zpos_property,