In fast switch mode the adv7180 (and similar) can lock onto a new signal
faster when switching between different inputs. As a downside though it is
no longer able to auto-detect the incoming format.

The fast switch mode is exposed as a boolean v4l control that allows
userspace applications to either enable or disable fast switch mode.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Federico Vaga <federico.vaga@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>