media: v4l: Add new 2X8 10-bit grayscale media bus code

The code will be called MEDIA_BUS_FMT_Y10_2X8_PADHI_LE.
It is similar to MEDIA_BUS_FMT_SBGGR10_2X8_PADHI_LE
but MEDIA_BUS_FMT_Y10_2X8_PADHI_LE describes grayscale
data.

Signed-off-by: Todor Tomov <todor.tomov@linaro.org>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>