mmap_mapper should operate on a buffer, not on a complete queue. So let
the videobuf-core find the correct buffer instead of duplicating that
code in each mmap_mapper implementation.

The dma-sg implementation has backwards compatibility code for handling
the V4L1_COMPAT layer. This code is now under the v4L1_COMPAT config option.
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>