JZ4740 and similar SoCs real-time clock driver

Required properties:

- compatible: One of:
  - "ingenic,jz4740-rtc" - for use with the JZ4740 SoC
  - "ingenic,jz4780-rtc" - for use with the JZ4780 SoC
- reg: Address range of rtc register set
- interrupts: IRQ number for the alarm interrupt
- clocks: phandle to the "rtc" clock
- clock-names: must be "rtc"

Optional properties:
- system-power-controller: To use this component as the
  system power controller
- reset-pin-assert-time-ms: Reset pin low-level assertion
  time after wakeup (default 60ms; range 0-125ms if RTC clock
  at 32 kHz)
- min-wakeup-pin-assert-time-ms: Minimum wakeup pin assertion
  time (default 100ms; range 0-2s if RTC clock at 32 kHz)

Example:

rtc@10003000 {
	compatible = "ingenic,jz4740-rtc";
	reg = <0x10003000 0x40>;

	interrupt-parent = <&intc>;
	interrupts = <32>;

	clocks = <&rtc_clock>;
	clock-names = "rtc";

	system-power-controller;
	reset-pin-assert-time-ms = <60>;
	min-wakeup-pin-assert-time-ms = <100>;
};
