Device-Tree bindings for MediaTek MT5896 SoC based RTC

Required properties:
- compatible	    : Should be
			"mediatek,mt5896-rtc" : for MT5896 SoC
- reg 		    : Specifies base physical address and size of the registers;
- interrupts	    : Should contain the interrupt for RTC alarm;
- clocks	    : Specifies list of clock specifiers, corresponding to
		      entries in clock-names property;
- clock-names	    : Should contain "rtc" entries
- default-cnt	    : Specifies the initial default time for RTC

Example:

rtc: rtc@1f002400 {
	compatible = "mediatek,mt5896-rtc";
	reg = <0 0x1c020600 0 0x200>,
	      <0 0x1c020200 0 0x200>;
	interrupt-parent = <&mtk_intc2_irq_high>;
	interrupts = <0x0 0x18 0x4>;
	xtal = <12000000>;
	freq = <1>;
	default-cnt = <946684800>;
};
