iio: adc: Add viperboard adc driver

This adds the mfd cell to use the adc part of the Nano River Technologies
viperboard.

Signed-off-by: Lars Poeschel <poeschel@lemonage.de>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 1401ed1..bb30537 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -67,4 +67,11 @@
 	  Say yes here to build support for Texas Instruments ADC
 	  driver which is also a MFD client.
 
+config VIPERBOARD_ADC
+	tristate "Viperboard ADC support"
+	depends on MFD_VIPERBOARD && USB
+	help
+	  Say yes here to access the ADC part of the Nano River
+	  Technologies Viperboard.
+
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