ST M41T80 family of RTC and compatible

Required properties:
- compatible: should be one of:
	"st,m41t62",
	"st,m41t65",
	"st,m41t80",
	"st,m41t81",
	"st,m41t81s",
	"st,m41t82",
	"st,m41t83",
	"st,m41t84",
	"st,m41t85",
	"st,m41t87",
	"microcrystal,rv4162",
- reg: I2C bus address of the device

Optional properties:
- interrupts: rtc alarm interrupt.
- clock-output-names: From common clock binding to override the default output
                      clock name
- wakeup-source: Enables wake up of host system on alarm

Optional child node:
- clock: Provide this if the square wave pin is used as boot-enabled fixed clock.

Example:
	rtc@68 {
		compatible = "st,m41t80";
		reg = <0x68>;
		interrupt-parent = <&UIC0>;
		interrupts = <0x9 0x8>;

		clock {
			compatible = "fixed-clock";
			#clock-cells = <0>;
			clock-frequency = <32768>;
		};
	};