media: mediatek: vcodec: Alloc DMA memory with DMA_ATTR_ALLOC_SINGLE_PAGES

As talked about in commit 14d3ae2e ("ARM: 8507/1: dma-mapping: Use
DMA_ATTR_ALLOC_SINGLE_PAGES hint to optimize alloc"), it doesn't
really make sense to try to allocate contiguous chunks of memory for
video encoding/decoding. Let's switch the Mediatek vcodec driver to
pass DMA_ATTR_ALLOC_SINGLE_PAGES and take some of the stress off the
memory subsystem.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Tested-by: Fei Shao <fshao@chromium.org>
Reviewed-by: Fei Shao <fshao@chromium.org>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Sebastian Fricke <sebastian.fricke@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>