Device-Tree bindings for mixer driver

Required properties:
- compatible: value should be "samsung,exynos5-mixer".
- reg: physical base address of the mixer and length of memory mapped
	region.
- interrupts: interrupt number to the cpu.

Example:

	mixer {
		compatible = "samsung,exynos5-mixer";
		reg = <0x14450000 0x10000>;
		interrupts = <0 94 0>;
	};
