V4L/DVB: mt9v011: add enum/try/s_mbus_fmt support

Note that this driver is only used by em28xx and that em28xx does not
actually call the enum/try/s_fmt ops of mt9v011. So these functions
have never been tested.

And in fact the driver really implements cropping instead of scaling. So it
seems to be doing the wrong thing :-(

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>