sh: add a YUV422 output data format, that is also supported by LCDC

The LCDC block is allowed to use one of the two output data formats, when used
with MIPI DSI: RGB24 and YUV422. YUV422 is not currently handled by the LCDC
driver, but we have to add a define for it for MIPI.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>