Device-Tree bindings for MediaTek SoC based RTC

Required properties:
- compatible	    : Should be "mediatek,mt2712-rtc" : for MT2712 SoC
- reg 		    : Specifies base physical address and size of the registers;
- interrupts	    : Should contain the interrupt for RTC alarm;

Example:

rtc: rtc@10011000 {
	compatible = "mediatek,mt2712-rtc";
	reg = <0 0x10011000 0 0x1000>;
	interrupts = <GIC_SPI 239 IRQ_TYPE_LEVEL_LOW>;
};
