dt-bindings: iio: adc: add Meson8m2 support

The Amlogic Meson SAR ADC implementation on the Meson8m2 SoC is
identical to the Meson8b variant. Add a compatible string to indicate
that we support the SAR ADC on the Meson8m2 SoC.
Signed-off-by: NMartin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: NJonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/amlogic,meson-saradc.txt

@@ -4,6 +4,7 @@ Required properties:
 - compatible:	depending on the SoC this should be one of:
 			- "amlogic,meson8-saradc" for Meson8
 			- "amlogic,meson8b-saradc" for Meson8b
+			- "amlogic,meson8m2-saradc" for Meson8m2
 			- "amlogic,meson-gxbb-saradc" for GXBB
 			- "amlogic,meson-gxl-saradc" for GXL
 			- "amlogic,meson-gxm-saradc" for GXM