ASoC: add DT bindings for Microchip S/PDIF TX Controller

This patch adds DT bindings for the new Microchip S/PDIF TX Controller
embedded inside sama7g5 SoCs.
Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200909145348.367033-1-codrin.ciubotariu@microchip.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/mchp,spdiftx.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/sound/mchp,spdiftx.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Microchip S/PDIF Tx Controller Device Tree Bindings
+
+maintainers:
+  - Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
+
+description:
+        The Microchip Sony/Philips Digital Interface Transmitter is a
+        serial port compliant with the IEC-60958 standard.
+
+properties:
+  "#sound-dai-cells":
+    const: 0
+
+  compatible:
+    const: microchip,sama7g5-spdiftx
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  clocks:
+    items:
+      - description: Peripheral Bus Clock
+      - description: Generic Clock
+
+  clock-names:
+    items:
+      - const: pclk
+      - const: gclk
+
+  dmas:
+    description: TX DMA Channel
+    maxItems: 1
+
+  dma-names:
+    const: tx
+
+required:
+  - "#sound-dai-cells"
+  - compatible
+  - reg
+  - interrupts
+  - clocks
+  - clock-names
+  - dmas
+  - dma-names
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/at91.h>
+    #include <dt-bindings/dma/at91.h>
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+
+    spdiftx@e1618000 {
+        #sound-dai-cells = <0>;
+        compatible = "microchip,sama7g5-spdiftx";
+        reg = <0xe1618000 0x4000>;
+        interrupts = <GIC_SPI 85 IRQ_TYPE_LEVEL_HIGH>;
+        dmas = <&dma0 AT91_XDMAC_DT_PERID(50)>;
+        dma-names = "tx";
+        clocks = <&pmc PMC_TYPE_PERIPHERAL 85>, <&pmc PMC_TYPE_GCK 85>;
+        clock-names = "pclk", "gclk";
+        pinctrl-names = "default";
+        pinctrl-0 = <&pinctrl_spdiftx_default>;
+    };