Clock bindings for ST-Ericsson Ux500 clocks

Required properties :
- compatible : shall contain only one of the following:
  "stericsson,u8500-clks"
  "stericsson,u8540-clks"
  "stericsson,u9540-clks"
- reg : shall contain base register location and length for
  CLKRST1, 2, 3, 5, and 6 in an array. Note the absence of
  CLKRST4, which does not exist.

Required subnodes:
- prcmu-clock: a subnode with one clock cell for PRCMU (power,
  reset, control unit) clocks. The cell indicates which PRCMU
  clock in the prcmu-clock node the consumer wants to use.
- prcc-periph-clock: a subnode with two clock cells for
  PRCC (programmable reset- and clock controller) peripheral clocks.
  The first cell indicates which PRCC block the consumer
  wants to use, possible values are 1, 2, 3, 5, 6. The second
  cell indicates which clock inside the PRCC block it wants,
  possible values are 0 thru 31.
- prcc-kernel-clock: a subnode with two clock cells for
  PRCC (programmable reset- and clock controller) kernel clocks
  The first cell indicates which PRCC block the consumer
  wants to use, possible values are 1, 2, 3, 5, 6. The second
  cell indicates which clock inside the PRCC block it wants,
  possible values are 0 thru 31.
- rtc32k-clock: a subnode with zero clock cells for the 32kHz
  RTC clock.
- smp-twd-clock: a subnode for the ARM SMP Timer Watchdog cluster
  with zero clock cells.

Example:

clocks {
	compatible = "stericsson,u8500-clks";
	/*
	 * Registers for the CLKRST block on peripheral
	 * groups 1, 2, 3, 5, 6,
	 */
	reg = <0x8012f000 0x1000>, <0x8011f000 0x1000>,
	    <0x8000f000 0x1000>, <0xa03ff000 0x1000>,
	    <0xa03cf000 0x1000>;

	prcmu_clk: prcmu-clock {
		#clock-cells = <1>;
	};

	prcc_pclk: prcc-periph-clock {
		#clock-cells = <2>;
	};

	prcc_kclk: prcc-kernel-clock {
		#clock-cells = <2>;
	};

	rtc_clk: rtc32k-clock {
		#clock-cells = <0>;
	};

	smp_twd_clk: smp-twd-clock {
		#clock-cells = <0>;
	};
};