CHROMIUM: vb2: Store dma_dir in vb2_queue.

CHROMIUM: vb2: Store dma_dir in vb2_queue.

Store dma_dir in struct vb2_queue and reuse it, instead of recalculating
it each time.

Signed-off-by: Pawel Osciak <posciak@chromium.org>
BUG=chrome-os-partner:45346
TEST=video playback

Reviewed-on: https://chromium-review.googlesource.com/300725
Commit-Ready: Pawel Osciak <posciak@chromium.org>
Tested-by: Pawel Osciak <posciak@chromium.org>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Reviewed-by: Owen Lin <owenlin@chromium.org>
Conflicts:
	drivers/media/v4l2-core/videobuf2-core.c

Change-Id: Ia5405cd758ffef0b0319d184a2f32699ebc805ea
Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Signed-off-by: Yakir Yang <ykk@rock-chips.com>