Device-Tree bindings for drm hdmi driver

Required properties:
- compatible: value should be "samsung,exynos5-hdmi".
- reg: physical base address of the hdmi and length of memory mapped
	region.
- interrupts: interrupt number to the cpu.
- hpd-gpio: following information about the hotplug gpio pin.
	a) phandle of the gpio controller node.
	b) pin number within the gpio controller.
	c) pin function mode.
	d) optional flags and pull up/down.
	e) drive strength.

Example:

	hdmi {
		compatible = "samsung,exynos5-hdmi";
		reg = <0x14530000 0x100000>;
		interrupts = <0 95 0>;
		hpd-gpio = <&gpx3 7 0xf 1 3>;
	};