[media] vivid: turn this into a platform_device

This turns this driver into a platform device. This ensures that it
appears in /sys/bus/platform_device since it now has a proper parent
device.

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