dt-bindings: soc: imx: Add binding doc for spba bus

Add binding doc for fsl,spba-bus.

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

Documentation/devicetree/bindings/bus/fsl,spba-bus.yaml

@@ -0,0 +1,68 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/bus/fsl,spba-bus.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Shared Peripherals Bus Interface
+
+maintainers:
+  - Shawn Guo <shawnguo@kernel.org>
+
+description: |
+  A simple bus enabling access to shared peripherals.
+
+  The "spba-bus" follows the "simple-bus" set of properties, as
+  specified in the Devicetree Specification.  It is an extension of
+  "simple-bus" because the SDMA controller uses this compatible flag to
+  determine which peripherals are available to it and the range over which
+  the SDMA can access.  There are no special clocks for the bus, because
+  the SDMA controller itself has its interrupt and clock assignments.
+
+select:
+  properties:
+    compatible:
+      contains:
+        const: fsl,spba-bus
+  required:
+    - compatible
+
+properties:
+  $nodename:
+    pattern: "^spba-bus(@[0-9a-f]+)?$"
+
+  compatible:
+    items:
+      - const: fsl,spba-bus
+      - const: simple-bus
+
+  '#address-cells':
+    enum: [ 1, 2 ]
+
+  '#size-cells':
+    enum: [ 1, 2 ]
+
+  reg:
+    maxItems: 1
+
+  ranges: true
+
+required:
+  - compatible
+  - '#address-cells'
+  - '#size-cells'
+  - reg
+  - ranges
+
+additionalProperties:
+  type: object
+
+examples:
+  - |
+    spba-bus@30000000 {
+        compatible = "fsl,spba-bus", "simple-bus";
+        #address-cells = <1>;
+        #size-cells = <1>;
+        reg = <0x30000000 0x100000>;
+        ranges;
+    };