[media] cx25821: drop cx25821-video-upstream-ch2.c/h

cx25821-video-upstream_ch2.c/h is practically identical to cx25821-video-upstream.c/h
so add support for ch2 into cx25821-video-upstream.c instead.
After this we can replace the custom ioctls with a proper write() interface.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>