media: uapi: add MEDIA_BUS_FMT_METADATA_FIXED media bus format.

MEDIA_BUS_FMT_METADATA_FIXED should be used when
the same driver handles both sides of the link and
the bus format is a fixed metadata format that is
not configurable from userspace.
The width and height will be set to 0 for this format.

Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
Acked-by: Helen Koike <helen.koike@collabora.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>