Allow userspace applications to subscribe to control change events. This
can e.g. be used to monitor the 5V detect control to be notified when a
source is connected or disconnected.
Signed-off-by: NLars-Peter Clausen <lars@metafoo.de>
Signed-off-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@osg.samsung.com>