dt-bindings: display: synopsys, dw-hdmi: Document ddc-i2c-bus in core

dt-bindings: display: synopsys, dw-hdmi: Document ddc-i2c-bus in core

The DW HDMI driver core is responsible for parsing the 'ddc-i2c-bus' property,
move the property description into the DW HDMI common DT schema too, so this
property can be used on all devices integrating the DW HDMI core.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240515062753.111746-1-marex@denx.de