drm/sun4i: hdmi: Add support for A31's HDMI controller

The HDMI controller found in the A31 SoCs is slightly different
from the one already supported, which is found in the A10s:

  - Need different initial values for the PLL related registers

  - Different behavior of the DDC and TMDS clocks

  - Different register layout for the DDC portion

  - Separate DDC parent clock

This patch adds support for it.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171010032008.682-10-wens@csie.org