clk: add clock-indices support

  clocks by index. The names should reflect the clock output signal

  names for the device.

clock-indices:	   If the identifyng number for the clocks in the node

		   is not linear from zero, then the this mapping allows

		   the mapping of identifiers into the clock-output-names

		   array.

For example, if we have two clocks <&oscillator 1> and <&oscillator 3>:

	oscillator {

		compatible = "myclocktype";

		#clock-cells = <1>;

		clock-indices = <1>, <3>;

		clock-output-names = "clka", "clkb";

	}

	This ensures we do not have any empty nodes in clock-output-names

==Clock consumers==

Required properties:

const char *of_clk_get_parent_name(struct device_node *np, int index)

{

	struct of_phandle_args clkspec;

	struct property *prop;

	const char *clk_name;

	const __be32 *vp;

	u32 pv;

	int rc;

	int count;

	if (index < 0)

		return NULL;

	if (rc)

		return NULL;

	index = clkspec.args_count ? clkspec.args[0] : 0;

	count = 0;

	/* if there is an indices property, use it to transfer the index

	 * specified into an array offset for the clock-output-names property.

	 */

	of_property_for_each_u32(clkspec.np, "clock-indices", prop, vp, pv) {

		if (index == pv) {

			index = count;

			break;

		}

		count++;

	}

	if (of_property_read_string_index(clkspec.np, "clock-output-names",

					  clkspec.args_count ? clkspec.args[0] : 0,

					  index,

					  &clk_name) < 0)

		clk_name = clkspec.np->name;