Add support for the test_pattern control and the h/vflip controls.

This makes it possible to switch to more interesting test patterns and to
test control handling in v4l-subdevs.

There are more tpg-related controls that can be added, but this is a good
start.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
[hans.verkuil@cisco.com: fix small whitespace checkpatch warning]
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>