drm/mediatek: Remove unused GEM DMA header include

No longer needed since the removal of dependency on DMA helper.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reported-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20230127165409.3512501-1-robdclark@gmail.com/


Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>