[media] videodev2.h: split off controls into v4l2-controls.h

During the 2012 Media Workshop it was decided to split off the control
definitions into their own v4l2-controls.h header, included by videodev2.h.
Because controls make up such a large part of V4L2 they made it hard
to read videodev2.h. Splitting off the control definitions makes life
easier.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>