dt-bindings: iio/adc: Add touchscreen idx for JZ47xx SoC ADC

Introduce support for touchscreen channels found in JZ47xx SoCs.
Signed-off-by: Artur Rojek <contact@artur-rojek.eu>
Tested-by: Paul Cercueil <paul@crapouillou.net>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

include/dt-bindings/iio/adc/ingenic,adc.h

@@ -7,5 +7,11 @@
 #define INGENIC_ADC_AUX		0
 #define INGENIC_ADC_BATTERY	1
 #define INGENIC_ADC_AUX2	2
+#define INGENIC_ADC_TOUCH_XP	3
+#define INGENIC_ADC_TOUCH_YP	4
+#define INGENIC_ADC_TOUCH_XN	5
+#define INGENIC_ADC_TOUCH_YN	6
+#define INGENIC_ADC_TOUCH_XD	7
+#define INGENIC_ADC_TOUCH_YD	8
 
 #endif