dt-bindings: sun4i-drm: add compatible for R40 HDMI PHY

The Allwinner R40 HDMI PHY is currently the only one that seems to be
able to select between two PLL inputs.

Add a compatible string for it, and the pll-1 clock input definition.
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180916043409.62374-3-icenowy@aosc.io

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

@@ -107,6 +107,7 @@ Required properties:
   - compatible: value must be one of:
     * allwinner,sun8i-a83t-hdmi-phy
     * allwinner,sun8i-h3-hdmi-phy
+    * allwinner,sun8i-r40-hdmi-phy
     * allwinner,sun50i-a64-hdmi-phy
   - reg: base address and size of memory-mapped region
   - clocks: phandles to the clocks feeding the HDMI PHY
@@ -116,9 +117,9 @@ Required properties:
   - resets: phandle to the reset controller driving the PHY
   - reset-names: must be "phy"
 
-H3 and A64 HDMI PHY require additional clocks:
+H3, A64 and R40 HDMI PHY require additional clocks:
   - pll-0: parent of phy clock
-  - pll-1: second possible phy clock parent (A64 only)
+  - pll-1: second possible phy clock parent (A64/R40 only)
 
 TV Encoder
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