iio: adc: add driver for MCP3204/08 12-bit ADC

This adds support for Microchip's 12 bit AD converters MCP3204 and
MCP3208. These chips communicates over SPI and supports single-ended
and pseudo-differential configurations.

Signed-off-by: Oskar Andero <oskar.andero@gmail.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index ab0767e6..93129ec 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -133,6 +133,16 @@
 	  max11646, max11647) Provides direct access via sysfs and buffered
 	  data via the iio dev interface.
 
+config MCP320X
+	tristate "Microchip Technology MCP3204/08"
+	depends on SPI
+	help
+	  Say yes here to build support for Microchip Technology's MCP3204 or
+	  MCP3208 analog to digital converter.
+
+	  This driver can also be built as a module. If so, the module will be
+	  called mcp320x.
+
 config TI_ADC081C
 	tristate "Texas Instruments ADC081C021/027"
 	depends on I2C