drm/sun4i: dw-hdmi: Add quirk for setting TMDS clock

It turns out that H6 HDMI BSP kernel driver doesn't change TMDS rate at
all. At this point it is not clear whether it is just not necessary or
it would cause some kind of issues.

Add a quirk for it.

Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181104182705.18047-18-jernej.skrabec@siol.net