dt-bindings: rtc: convert MT7622 RTC to the json-schema

This helps validating DTS files. Introduced changes:
1. Reworded title
2. Dropper redundant properties descriptions
3. Added required #include-s and adjusted "reg" in example

Signed-off-by: Rafał Miłecki <[e-mail]>
Reviewed-by: Conor Dooley <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexandre Belloni <[e-mail]>

Documentation/devicetree/bindings/rtc/mediatek,mt7622-rtc.yaml

···
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/rtc/mediatek,mt7622-rtc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: MediaTek MT7622 on-SoC RTC
+
+allOf:
+  - $ref: rtc.yaml#
+
+maintainers:
+  - Sean Wang <[e-mail]>
+
+properties:
+  compatible:
+    items:
+      - const: mediatek,mt7622-rtc
+      - const: mediatek,soc-rtc
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+  clock-names:
+    const: rtc
+
+required:
+  - reg
+  - interrupts
+  - clocks
+  - clock-names
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/mt7622-clk.h>
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+
+    rtc@10212800 {
+        compatible = "mediatek,mt7622-rtc", "mediatek,soc-rtc";
+        reg = <0x10212800 0x200>;
+        interrupts = <GIC_SPI 129 IRQ_TYPE_LEVEL_LOW>;
+        clocks = <&topckgen CLK_TOP_RTC>;
+        clock-names = "rtc";
+    };

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";
-};