Device Tree Clock bindings for Altera's SoCFPGA platform

This binding uses the common clock binding[1].

[1] Documentation/devicetree/bindings/clock/clock-bindings.txt

Required properties:
- compatible : shall be one of the following:
	"altr,socfpga-pll-clock" - for a PLL clock
	"altr,socfpga-perip-clock" - The peripheral clock divided from the
		PLL clock.
	"altr,socfpga-gate-clk" - Clocks that directly feed peripherals and
		can get gated.

- reg : shall be the control register offset from CLOCK_MANAGER's base for the clock.
- clocks : shall be the input parent clock phandle for the clock. This is
	either an oscillator or a pll output.
- #clock-cells : from common clock binding, shall be set to 0.

Optional properties:
- fixed-divider : If clocks have a fixed divider value, use this property.
- clk-gate : For "socfpga-gate-clk", clk-gate contains the gating register
        and the bit index.
- div-reg : For "socfpga-gate-clk", div-reg contains the divider register, bit shift,
        and width.
