[media] v4l: videodev2: add buffer size to SDR format

Add buffer size field to struct v4l2_sdr_format. It is used for
negotiate streaming buffer size between application and driver.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>