media: tvp5150: add v4l2-event support

Currently the driver notifies internal subdevs if the signal is locked
or not. This information is also useful for userpace applications e.g. to
switch to another input device upon a signal lost event.

This commit adds the support for the userspace to subscribe to the
V4L2_EVENT_SOURCE_CHANGE and V4L2_EVENT_CTRL events.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>