[media] fsl-viu: replace .ioctl by .unlocked_ioctl

Use the core-assisted locking in fsl-viu driver and switch
to .unlocked_ioctl.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>