V4L/DVB (13468): v4l2 doc: Added ROTATE and BG_COLOR control documentation

Signed-off-by: Vaibhav Hiremath <hvaibhav@ti.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>