fbdev: sh_mobile_lcdc: Add YUV framebuffer support

Supports YCbCr420sp, YCbCr422sp, and YCbCr44sp, formats
(bpp = 12, 16, and 24) respectively.

When double-buffering both Y planes appear before the C planes (Y-Y-C-C),
as opposed to  Y-C-Y-C.

Set .nonstd in struct sh_mobile_lcdc_chan_cfg to enable YUV mode, and use
.bpp to distiguish between the 3 modes.
The value of .nonstd is copied to bits 16-31 of LDDFR in the LCDC and
should be set accordingly.
.nonstd must be set to 0 for RGB mode.

Due to the encoding of YUV data, the framebuffer will clear to green
instead of black.

In YUV 420 mode, panning is only possible in 2 line increments.
Additionally in YUV 420 mode the vertical resolution of the framebuffer
must be an even number.

Signed-off-by: Damian Hobson-Garcia <dhobsong@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>