V4L/DVB (8427): videodev: split off the ioctl handling into v4l2-ioctl.c

V4L/DVB (8427): videodev: split off the ioctl handling into v4l2-ioctl.c

videodev.c became top-heavy so all the ioctl processing has been split off
into v4l2-ioctl.c. This means videodev.c is back to its original purpose:
creating and registering v4l devices.

Since videodev.c and v4l2-ioctl.c should still remain one module (as least
for now) I also had to rename videodev.c to v4l2-dev.c to prevent a
circular dependency when building a videodev.ko module. This is not a bad
thing, since the source and header now have the same name. And the v4l2-
prefix is useful to see which sources are generic v4l2 support code.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>