drm/mediatek: Allow build with COMPILE_TEST=y

Allow mediatek to be built with COMPILE_TEST=y for greater
coverage. Builds fine on x86/x86_64 at least.

Cc: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: linux-mediatek@lists.infradead.org
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241003111851.10453-10-ville.syrjala@linux.intel.com


Reviewed-by: CK Hu <ck.hu@mediatek.com>