Document V4L2_SDR_FMT_RU12LE format. It is real unsigned 12-bit
little endian sample inside 16-bit space. Used by software defined
radio devices.
Signed-off-by: NAntti Palosaari <crope@iki.fi>
Signed-off-by: NMauro Carvalho Chehab <m.chehab@samsung.com>