dt-bindings: mfd: Add Broadcom's Timer-Watchdog block

It's a block implementing few time related functions depending on a
(SoC specific) variant. At this point there is ready binding for a
watchdog only. Work on remaining subblocks (e.g. "reg" based reboot) is
in progress.

Signed-off-by: Rafał Miłecki <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/devicetree/bindings/mfd/brcm,twd.yaml

···
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mfd/brcm,twd.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Broadcom's Timer-Watchdog (aka TWD)
+
+maintainers:
+  - Rafał Miłecki <[e-mail]>
+
+description: |
+  Broadcom has a Timer-Watchdog block used in multiple SoCs (e.g., BCM4908,
+  BCM63xx, BCM7038). There are few variants available (they differ slightly in
+  registers layout). This block consists of: timers, watchdog and optionally a
+  software reset handler.
+
+properties:
+  compatible:
+    items:
+      - enum:
+          - brcm,bcm4908-twd
+          - brcm,bcm7038-twd
+      - const: simple-mfd
+      - const: syscon
+
+  reg:
+    maxItems: 1
+
+  ranges: true
+
+  "#address-cells":
+    const: 1
+
+  "#size-cells":
+    const: 1
+
+patternProperties:
+  '^watchdog@[a-f0-9]+$':
+    $ref: /schemas/watchdog/brcm,bcm7038-wdt.yaml
+
+additionalProperties: false
+
+required:
+  - reg
+
+examples:
+  - |
+    timer-mfd@ff800400 {
+        compatible = "brcm,bcm4908-twd", "simple-mfd", "syscon";
+        reg = <0xff800400 0x4c>;
+        ranges = <0x00000000 0xff800400 0x4c>;
+
+        #address-cells = <1>;
+        #size-cells = <1>;
+
+        watchdog@28 {
+            compatible = "brcm,bcm7038-wdt";
+            reg = <0x28 0x8>;
+        };
+    };