drm/mediatek: Fix Kconfig warning

WARNING: unmet direct dependencies detected for MTK_MMSYS
  Depends on [n]: (ARCH_MEDIATEK [=y] || COMPILE_TEST [=n]) && COMMON_CLK_MT8173_MMSYS [=n]
  Selected by [y]:
  - DRM_MEDIATEK [=y] && HAS_IOMEM [=y] && DRM [=y] && (ARCH_MEDIATEK [=y] || ARM && COMPILE_TEST [=n]) && COMMON_CLK [=y] && HAVE_ARM_SMCCC [=y] && OF [=y]

Make DRM_MEDIATEK depend on MTK_MMSYS to fix this.

Fixes: 2c758e30 ("soc / drm: mediatek: Move routing control to mmsys device")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>

drivers/gpu/drm/mediatek/Kconfig

@@ -6,12 +6,12 @@ config DRM_MEDIATEK
 	depends on COMMON_CLK
 	depends on HAVE_ARM_SMCCC
 	depends on OF
+	depends on MTK_MMSYS
 	select DRM_GEM_CMA_HELPER
 	select DRM_KMS_HELPER
 	select DRM_MIPI_DSI
 	select DRM_PANEL
 	select MEMORY
-	select MTK_MMSYS
 	select MTK_SMI
 	select VIDEOMODE_HELPERS
 	help