[media] V4L: mx3_camera: convert to videobuf2

Now that soc-camera supports videobuf API v1 and v2, camera-host drivers
can be converted to videobuf2 individually. This patch converts the
mx3_camera driver.
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>