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