V4L/DVB: [v5,2/2] v4l: Add a mem-to-mem videobuf framework test device

This is a virtual device driver for testing the memory-to-memory framework.

This virtual device uses in-memory buffers for both its source and destination.
It is capable of multi-instance, multi-buffer-per-transaction operation
(via the mem2mem framework).

[mchehab@redhat.com: use videobuf_queue_to_vaddr instead of the removed videobuf_queue_to_vmalloc]
Signed-off-by: Pawel Osciak <p.osciak@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Vaibhav Hiremath <hvaibhav@ti.com>
Tested-by: Vaibhav Hiremath <hvaibhav@ti.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>