V4L/DVB (11097): use video_ioctl2 as ioctl handler directly

The encoder commands ioctls are available in v4l2_ioctl_ops. Use them
and get rid of the custom ioctl handler and use video_ioctl2.

Signed-off-by: Janne Grunau <j@jannau.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>