media: videobuf2: handle non-contiguous DMA allocations

This adds support for the new noncontiguous DMA API, which
requires allocators to have two execution branches: one
for the current API, and one for the new one.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>