staging:iio:adc: Add AD7791 driver

This patch adds support for the Analog Devices AD7787, AD7788, AD7789, AD7790
and AD7791 Sigma Delta Analog-to-Digital converters.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

include/linux/platform_data/ad7791.h

@@ -0,0 +1,17 @@
+#ifndef __LINUX_PLATFORM_DATA_AD7791__
+#define __LINUX_PLATFORM_DATA_AD7791__
+
+/**
+ * struct ad7791_platform_data - AD7791 device platform data
+ * @buffered: If set to true configure the device for buffered input mode.
+ * @burnout_current: If set to true the 100mA burnout current is enabled.
+ * @unipolar: If set to true sample in unipolar mode, if set to false sample in
+ *		bipolar mode.
+ */
+struct ad7791_platform_data {
+	bool buffered;
+	bool burnout_current;
+	bool unipolar;
+};
+
+#endif