Binding for simple multiplier clock.

This binding uses the common clock binding[1].  It assumes a
register-mapped adjustable clock rate multiplier that does not gate and has
only one input clock or parent.  By default the value programmed into
the register is one less than the actual multiplier value.  E.g:

register value		actual multiplier value
0			1
1			2
2			3

This assumption may be modified by the following optional properties:

index-starts-at-one - valid multiplier values start at 1, not the default
of 0.  E.g:
register value		actual multiplier value
1			1
2			2
3			3

index-power-of-two - valid multiplier values are powers of two.  E.g:
register value		actual multiplier value
0			1
1			2
2			4

index-allow-zero - same as index_one, but zero is multiply-by-1.  E.g:
register value		actual multiplier value
0			1
1			1
2			2

Additionally a table of valid multipliers may be supplied like so:

	table = <4 0>, <8, 1>;

where the first value in the pair is the multiplier and the second value is
the programmed register bitfield.

The binding must also provide the register to control the multiplier and
the mask for the corresponding control bits.  Optionally the number of
bits to shift that mask, if necessary.  If the shift value is missing it
is the same as supplying a zero shift.

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

Required properties:
- compatible : shall be "multiplier-clock".
- #clock-cells : from common clock binding; shall be set to 0.
- clocks : link to phandle of parent clock
- reg : base address for register controlling adjustable multiplier
- bit-mask : arbitrary bitmask for programming the adjustable multiplier

Optional properties:
- clock-output-names : from common clock binding.
- table : array of integer pairs defining multipliers & bitfield values
- bit-shift : number of bits to shift the bit-mask, defaults to
  (ffs(mask) - 1) if not present
- index-starts-at-one : valid multiplier programming starts at 1, not zero
- index-power-of-two : valid multiplier programming must be a power of two
- index-allow-zero : implies index-one, and programming zero results in
  multiply-by-one
- index-max-mult-at-zero : same as index-starts-at-one, but the value
  of zero implies a multiplier of 2^width of the register field.

Examples:
	clock_foo: clock_foo at 4a008100 {
		compatible = "multiplier-clock";
		#clock-cells = <0>;
		clocks = <&clock_baz>;
		reg = <0x4a008100 0x4>
		mask = <0x3>
	};

	clock_bar: clock_bar at 4a008108 {
		#clock-cells = <0>;
		compatible = "multiplier-clock";
		clocks = <&clock_foo>;
		reg = <0x4a008108 0x4>;
		mask = <0x1>;
		shift = <0>;
		table = < 4 0 >, < 8 1 >;
	};