va: allocator: dma: Fail when mapping the non-linear buffer.

va: allocator: dma: Fail when mapping the non-linear buffer.

The current way of DMA buffer mapping is simply forwarding the job
to parent's map function, which is a mmap(). That can not handle the
non-linear buffers, such as tiling, compressed, etc. The incorrect
mapping of such buffers causes broken images, which are recognized
as bugs. We should directly block this kind of mapping to avoid the
misunderstanding.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2353>