dt-bindings: mmc: Add Actions Semi SD/MMC/SDIO controller binding

Add devicetree YAML binding for Actions Semi Owl SoC's SD/MMC/SDIO
controller.
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/owl-mmc.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mmc/owl-mmc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Actions Semi Owl SoCs SD/MMC/SDIO controller
+
+allOf:
+  - $ref: "mmc-controller.yaml"
+
+maintainers:
+  - Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
+
+properties:
+  compatible:
+    const: actions,owl-mmc
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  clocks:
+    minItems: 1
+
+  resets:
+    maxItems: 1
+
+  dmas:
+    maxItems: 1
+
+  dma-names:
+    const: mmc
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - clocks
+  - resets
+  - dmas
+  - dma-names
+
+examples:
+  - |
+    mmc0: mmc@e0330000 {
+        compatible = "actions,owl-mmc";
+        reg = <0x0 0xe0330000 0x0 0x4000>;
+        interrupts = <0 42 4>;
+        clocks = <&cmu 56>;
+        resets = <&cmu 23>;
+        dmas = <&dma 2>;
+        dma-names = "mmc";
+        bus-width = <4>;
+    };
+
+...