[media] solo6x10: convert encoder nodes 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As a consequence the ioctl op has been replaced by unlocked_ioctl.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.

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