[C61] add MAX98357A audio support

* audio over SAI3 interface
* sound works only at 48000Hz: this derives from SAI3 assigned clock rate.
* Test details:
  aplay --device sysdefault:CARD=max98457a /usr/share/sounds/alsa/Noise.wav

arch/arm64/boot/dts/seco/seco-imx8mm-c61.dts

@@ -141,6 +141,33 @@
 		regulator-always-on;
 	};
 
+	max98357a: audio-codec-0 {
+		compatible = "maxim,max98357a";
+		sdmode-gpios = <&pca6416_20 11 GPIO_ACTIVE_HIGH>;
+		sdmode,gpio-probe-only;
+		#sound-dai-cells = <0>;
+		status = "okay";
+	};
+
+	sound {
+		compatible = "simple-audio-card";
+		simple-audio-card,name = "max98457a";
+		simple-audio-card,format = "i2s";
+		simple-audio-card,frame-master = <&cpudai>;
+		simple-audio-card,bitclock-master = <&cpudai>;
+		simple-audio-card,widgets = "Speaker", "Speakers";
+		simple-audio-card,routing = "Speakers", "Speaker";
+		status = "okay";
+
+		cpudai: simple-audio-card,cpu {
+			sound-dai = <&sai3>;
+		};
+
+		simple-audio-card,codec {
+			sound-dai = <&max98357a>;
+		};
+	};
+
 	sound-micfil {
 		compatible = "fsl,imx-audio-micfil";
 		model = "imx-audio-micfil";
@@ -493,7 +520,10 @@
 	pinctrl-0 = <&pinctrl_sai3>;
 	assigned-clocks = <&clk IMX8MM_CLK_SAI3>;
 	assigned-clock-parents = <&clk IMX8MM_AUDIO_PLL1_OUT>;
-	assigned-clock-rates = <24576000>;
+	assigned-clock-rates = <196608000>;
+	fsl,sai-mclk-direction-output;
+	fsl,sai-synchronous-rx;
+	#sound-dai-cells = <0>;
 	status = "okay";
 };