dt-bindings: rtc: mediatek: add bindings for MediaTek SoC based RTC

Add device-tree binding for MediaTek SoC based RTC

Cc: [e-mail]
Signed-off-by: Sean Wang <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Alexandre Belloni <[e-mail]>

Documentation/devicetree/bindings/rtc/rtc-mt7622.txt

···
+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";
+};