ASoC: micfil: Add bindings for MICFIL DAI

Document the bindings for MICFIL DAI.
Signed-off-by: Cosmin-Gabriel Samoila <cosmin.samoila@nxp.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/fsl,micfil.txt

+NXP MICFIL Digital Audio Interface (MICFIL).
+
+The MICFIL digital interface provides a 16-bit audio signal from a PDM
+microphone bitstream in a configurable output sampling rate.
+
+Required properties:
+
+  - compatible		: Compatible list, contains "fsl,imx8mm-micfil"
+
+  - reg			: Offset and length of the register set for the device.
+
+  - interrupts		: Contains the micfil interrupts.
+
+  - clocks		: Must contain an entry for each entry in clock-names.
+
+  - clock-names		: Must include the "ipg_clk" for register access and
+			  "ipg_clk_app" for internal micfil clock.
+
+  - dmas		: Generic dma devicetree binding as described in
+			  Documentation/devicetree/bindings/dma/dma.txt.
+
+Example:
+micfil: micfil@30080000 {
+	compatible = "fsl,imx8mm-micfil";
+	reg = <0x0 0x30080000 0x0 0x10000>;
+	interrupts = <GIC_SPI 109 IRQ_TYPE_LEVEL_HIGH>,
+		     <GIC_SPI 110 IRQ_TYPE_LEVEL_HIGH>;
+	clocks = <&clk IMX8MM_CLK_PDM_IPG>,
+		 <&clk IMX8MM_CLK_PDM_ROOT>;
+	clock-names = "ipg_clk", "ipg_clk_app";
+	dmas = <&sdma2 24 26 0x80000000>;
+};