V4L/DVB (6061): ivtv: add VIDIOC_OVERLAY

Add VIDIOC_OVERLAY to enable/disable the OSD. Also add the OSD state to the
log status report.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>