dt-bindings: imx: ldb: Add ddc-i2c-bus property

Document the ddc-i2c-bus property used by imx-ldb driver to read EDID
information via I2C interface.

Signed-off-by: Akshay Bhat <akshay.bhat@timesys.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

Documentation/devicetree/bindings/display/imx/ldb.txt

@@ -62,6 +62,7 @@ Required properties:
    display-timings are used instead.
 
 Optional properties (required if display-timings are used):
+ - ddc-i2c-bus: phandle of an I2C controller used for DDC EDID probing
  - display-timings : A node that describes the display timings as defined in
    Documentation/devicetree/bindings/display/display-timing.txt.
  - fsl,data-mapping : should be "spwg" or "jeida"