drm: sti: allow to change hdmi ddc i2c adapter

Depending of the board configuration i2c for ddc could change,
this patch allow to use a phandle to specify which i2c controller to use.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
diff --git a/Documentation/devicetree/bindings/gpu/st,stih4xx.txt b/Documentation/devicetree/bindings/gpu/st,stih4xx.txt
index 2d150c3..8885d9e 100644
--- a/Documentation/devicetree/bindings/gpu/st,stih4xx.txt
+++ b/Documentation/devicetree/bindings/gpu/st,stih4xx.txt
@@ -69,6 +69,7 @@
   - clock-names: names of the clocks listed in clocks property in the same
     order.
   - hdmi,hpd-gpio: gpio id to detect if an hdmi cable is plugged or not.
+  - ddc: phandle of an I2C controller used for DDC EDID probing
 
 sti-hda:
   Required properties: