dt-bindings: power: document Broadcom's PMB binding

Broadcom's PMB is power controller used for disabling and enabling SoC
devices.
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

Documentation/devicetree/bindings/power/brcm,bcm-pmb.yaml

+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/power/brcm,bcm-pmb.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Broadcom PMB (Power Management Bus) controller
+
+description: This document describes Broadcom's PMB controller. It supports
+  powering various types of connected devices (e.g. PCIe, USB, SATA).
+
+maintainers:
+  - Rafał Miłecki <rafal@milecki.pl>
+
+properties:
+  compatible:
+    enum:
+      - brcm,bcm4908-pmb
+
+  reg:
+    description: register space of one or more buses
+    maxItems: 1
+
+  big-endian:
+    $ref: /schemas/types.yaml#/definitions/flag
+    description: Flag to use for block working in big endian mode.
+
+  "#power-domain-cells":
+    description: cell specifies device ID (see bcm-pmb.h)
+    const: 1
+
+required:
+  - reg
+  - "#power-domain-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/soc/bcm-pmb.h>
+
+    pmb: power-controller@802800e0 {
+        compatible = "brcm,bcm4908-pmb";
+        reg = <0x802800e0 0x40>;
+        #power-domain-cells = <1>;
+    };
+
+    foo {
+        power-domains = <&pmb BCM_PMB_PCIE0>;
+    };

include/dt-bindings/soc/bcm-pmb.h

+/* SPDX-License-Identifier: GPL-2.0-or-later OR MIT */
+
+#ifndef __DT_BINDINGS_SOC_BCM_PMB_H
+#define __DT_BINDINGS_SOC_BCM_PMB_H
+
+#define BCM_PMB_PCIE0				0x01
+#define BCM_PMB_PCIE1				0x02
+#define BCM_PMB_PCIE2				0x03
+#define BCM_PMB_HOST_USB			0x04
+
+#endif