[media] solo6x10: convert the display node to vb2

As a consequence the ioctl op has been replaced by unlocked_ioctl.
Since we are now using the core lock the locking scheme has been
simplified as well.
The main reason for converting this driver to vb2 was that the locking
scheme in v4l2.c was hopeless. It was easier to just convert the driver
then to try and salvage a threading and videobuf nightmare.
The videobuf2 framework is far, far superior compared to the old videobuf.

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