dt-bindings: power: renesas,rzg2l-sysc: Add DT binding documentation for SYSC controller

Add DT binding documentation for SYSC controller found on
RZ/G2{L,LC,UL} SoC's.

SYSC block contains the LSI_DEVID register which is used to retrieve
SoC product information.
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://lore.kernel.org/r/20210609163717.3083-2-prabhakar.mahadev-lad.rj@bp.renesas.comSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

Documentation/devicetree/bindings/power/renesas,rzg2l-sysc.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: "http://devicetree.org/schemas/power/renesas,rzg2l-sysc.yaml#"
+$schema: "http://devicetree.org/meta-schemas/core.yaml#"
+
+title: Renesas RZ/G2L System Controller (SYSC)
+
+maintainers:
+  - Geert Uytterhoeven <geert+renesas@glider.be>
+
+description:
+  The RZ/G2L System Controller (SYSC) performs system control of the LSI and
+  supports following functions,
+  - External terminal state capture function
+  - 34-bit address space access function
+  - Low power consumption control
+  - WDT stop control
+
+properties:
+  compatible:
+    enum:
+      - renesas,r9a07g044-sysc # RZ/G2{L,LC}
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    items:
+      - description: CA55/CM33 Sleep/Software Standby Mode request interrupt
+      - description: CA55 Software Standby Mode release request interrupt
+      - description: CM33 Software Standby Mode release request interrupt
+      - description: CA55 ACE Asynchronous Bridge Master/Slave interface deny request interrupt
+
+  interrupt-names:
+    items:
+      - const: lpm_int
+      - const: ca55stbydone_int
+      - const: cm33stbyr_int
+      - const: ca55_deny
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - interrupt-names
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+
+    sysc: system-controller@11020000 {
+            compatible = "renesas,r9a07g044-sysc";
+            reg = <0x11020000 0x10000>;
+            interrupts = <GIC_SPI 42 IRQ_TYPE_LEVEL_HIGH>,
+                         <GIC_SPI 43 IRQ_TYPE_LEVEL_HIGH>,
+                         <GIC_SPI 44 IRQ_TYPE_LEVEL_HIGH>,
+                         <GIC_SPI 45 IRQ_TYPE_LEVEL_HIGH>;
+            interrupt-names = "lpm_int", "ca55stbydone_int", "cm33stbyr_int",
+                              "ca55_deny";
+    };