drm/mediatek: Drop dependency on ARM

The recent attempt to make the MediaTek DRM driver build for non-ARM
compile tests made the driver unbuildable for arm64 platforms. Since
this is used on both ARM and arm64 platforms, just drop the dependency
on ARM.

Fixes: d2db0b8f ("drm/mediatek: Allow build with COMPILE_TEST=y")
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241029111309.737263-1-wenst@chromium.org


Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>