Device-Tree bindings for MediaTek SoC based RTC

Required properties:
- compatible	    : Should be
			"mediatek,mt7622-rtc", "mediatek,soc-rtc" : for MT7622 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

Example:

rtc: rtc@10212800 {
	compatible = "mediatek,mt7622-rtc",
		     "mediatek,soc-rtc";
	reg = <0 0x10212800 0 0x200>;
	interrupts = <GIC_SPI 129 IRQ_TYPE_LEVEL_LOW>;
	clocks = <&topckgen CLK_TOP_RTC>;
	clock-names = "rtc";
};
