media: mgb4: Added support for additional GMSL modules variants

Added support for GMSL modules variants 3 and 4. Variant 3 is the same as
variant 2 from the driver's point of view. Variant 4 has "hardwired" daisy
chain loopback outputs and thus missing the v4l2 outputs.

Signed-off-by: Martin Tůma <martin.tuma@digiteqautomotive.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>