Binding for IDT VersaClock 5,6 programmable i2c clock generators.

The IDT VersaClock 5 and VersaClock 6 are programmable i2c clock
generators providing from 3 to 12 output clocks.

==I2C device node==

Required properties:
- compatible:	shall be one of
		"idt,5p49v5923"
		"idt,5p49v5925"
		"idt,5p49v5933"
		"idt,5p49v5935"
		"idt,5p49v6901"
- reg:		i2c device address, shall be 0x68 or 0x6a.
- #clock-cells:	from common clock binding; shall be set to 1.
- clocks:	from common clock binding; list of parent clock handles,
		- 5p49v5923 and
		  5p49v5925 and
		  5p49v6901: (required) either or both of XTAL or CLKIN
					reference clock.
		- 5p49v5933 and
		- 5p49v5935: (optional) property not present (internal
					Xtal used) or CLKIN reference
					clock.
- clock-names:	from common clock binding; clock input names, can be
		- 5p49v5923 and
		  5p49v5925 and
		  5p49v6901: (required) either or both of "xin", "clkin".
		- 5p49v5933 and
		- 5p49v5935: (optional) property not present or "clkin".

==Mapping between clock specifier and physical pins==

When referencing the provided clock in the DT using phandle and
clock specifier, the following mapping applies:

5P49V5923:
	0 -- OUT0_SEL_I2CB
	1 -- OUT1
	2 -- OUT2

5P49V5933:
	0 -- OUT0_SEL_I2CB
	1 -- OUT1
	2 -- OUT4

5P49V5925 and
5P49V5935:
	0 -- OUT0_SEL_I2CB
	1 -- OUT1
	2 -- OUT2
	3 -- OUT3
	4 -- OUT4

5P49V6901:
	0 -- OUT0_SEL_I2CB
	1 -- OUT1
	2 -- OUT2
	3 -- OUT3
	4 -- OUT4

==Example==

/* 25MHz reference crystal */
ref25: ref25m {
	compatible = "fixed-clock";
	#clock-cells = <0>;
	clock-frequency = <25000000>;
};

i2c-master-node {

	/* IDT 5P49V5923 i2c clock generator */
	vc5: clock-generator@6a {
		compatible = "idt,5p49v5923";
		reg = <0x6a>;
		#clock-cells = <1>;

		/* Connect XIN input to 25MHz reference */
		clocks = <&ref25m>;
		clock-names = "xin";
	};
};

/* Consumer referencing the 5P49V5923 pin OUT1 */
consumer {
	...
	clocks = <&vc5 1>;
	...
}