media: vivid: loopback based on 'Connected To' controls

Instead of using hardwired video loopback limited to a single vivid
instance, use the new 'Connected To' controls to only loopback if an
HDMI or S-Video input is connected to another output, which can be
in another vivid instance. Effectively this emulates connecting and
disconnecting an HDMI/S-Video cable.

The Loop Video control is dropped since it has now been replaced by
the new 'Connected To' controls. The Display Present has also been
dropped since it no longer fits.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Co-developed-by: Dorcas Anono Litunya <anonolitunya@gmail.com>
Signed-off-by: Dorcas Anono Litunya <anonolitunya@gmail.com>