drm/mediatek: Remove dependency on GEM DMA helper

It appears that the dependency on the DMA helpers was only for
drm_gem_dma_vm_ops.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20230119224052.2879106-1-robdclark@gmail.com/


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