[media] media/v4l2-core: Add support for V4L2_PIX_FMT_Y16_BE

16 bit greyscale format, structured in Big Endian. Such a format can be
converted into a PMN image just by adding a header.

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>