Move the plane-related fields of struct rcar_du_device to their own
structure.
Signed-off-by: NLaurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

The R-Car Display Unit (DU) DRM driver supports both superposition
processors and all eight planes in RGB and YUV formats with alpha
blending.

Only VGA and LVDS encoders and connectors are currently supported.
Signed-off-by: NLaurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>