drm/mediatek: Disable tmds on mt2701

Without that patch if you use specific resolutions like 1280x1024,
I can see distortion in the output. It seems as if the
frequency for updating the pixel of the image is out of sync.

For initialization tmds needs to be active, but can be disabled after init
to fix blurry display

Signed-off-by: chunhui dai <chunhui.dai@mediatek.com>
Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
Tested-by: Frank Wunderlich <frank-w@public-files.de>
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>