drm: Renesas SH Mobile DRM driver

The SH Mobile LCD controller (LCDC) DRM driver supports the main
graphics plane in RGB and YUV formats, as well as the overlay planes (in
alpha-blending mode only).

Only flat panel outputs using the parallel interface are supported.
Support for SYS panels, HDMI and DSI is currently not implemented.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sascha Hauer <s.hauer@pengutronix.de>