iio: Add support for creating IIO devices via configfs

This is similar with support for creating triggers via configfs.
Devices will be hosted under:
	* /config/iio/devices

We allow users to register "device types" under:
	* /config/iio/devices/<device_types>/

Signed-off-by: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
index 505e921..6743b18 100644
--- a/drivers/iio/Kconfig
+++ b/drivers/iio/Kconfig
@@ -46,6 +46,14 @@
 	This value controls the maximum number of consumers that a
 	given trigger may handle. Default is 2.
 
+config IIO_SW_DEVICE
+	tristate "Enable software IIO device support"
+	select IIO_CONFIGFS
+	help
+	 Provides IIO core support for software devices. A software
+	 device can be created via configfs or directly by a driver
+	 using the API provided.
+
 config IIO_SW_TRIGGER
 	tristate "Enable software triggers support"
 	select IIO_CONFIGFS