ASoC: dt-bindings: add max98088 audio codec

This patch adds the bindings for maxim max98088/9 audio codec.
Signed-off-by: Andreas Färber <afaerber@suse.de>
[m.felsch@pengutronix.de: adapt commit message]
[m.felsch@pengutronix.de: adapt formatting]
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/maxim,max98088.txt

+MAX98088 audio CODEC
+
+This device supports I2C only.
+
+Required properties:
+
+- compatible: "maxim,max98088" or "maxim,max98089".
+- reg: The I2C address of the device.
+
+Example:
+
+max98089: codec@10 {
+	compatible = "maxim,max98089";
+	reg = <0x10>;
+};