[media] media: add missing 8-bit bayer formats and Y12

8-bit SGBRG and SRGGB media bus formats are missing, as well as the
12-bit grey format. Add them.

Signed-off-by: Michael Jones <michael.jones@matrix-vision.de>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>