dt-bindings: display: sun4i: Add binding for A31 HDMI controller

The HDMI controller in the A31 SoC is slightly different from the
earlier version. In addition to the TMDS clock and DDC controls,
this version now takes a second DDC clock input.

Add a compatible string for it, and add the DDC clock input to the
list of clocks required.
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171010032008.682-7-wens@csie.org

Documentation/devicetree/bindings/display/sunxi/sun4i-drm.txt

@@ -41,14 +41,17 @@ CEC. It is one end of the pipeline.
 Required properties:
   - compatible: value must be one of:
     * allwinner,sun5i-a10s-hdmi
+    * allwinner,sun6i-a31-hdmi
   - reg: base address and size of memory-mapped region
   - interrupts: interrupt associated to this IP
   - clocks: phandles to the clocks feeding the HDMI encoder
     * ahb: the HDMI interface clock
     * mod: the HDMI module clock
+    * ddc: the HDMI ddc clock (A31 only)
     * pll-0: the first video PLL
     * pll-1: the second video PLL
   - clock-names: the clock names mentioned above
+  - resets: phandle to the reset control for the HDMI encoder (A31 only)
   - dmas: phandles to the DMA channels used by the HDMI encoder
     * ddc-tx: The channel for DDC transmission
     * ddc-rx: The channel for DDC reception