Staging: IIO: Add generic ring buffer support to the IIO core

This provides a unified interface for hardware and software
ring buffers.

Changes since V2:
* Moved to a more consistent structure.  Now the ring buffer
  has an associated struct device which is a child of the
  relevant iio_dev.  This in turn has two children, one
  for the event interface and one for the access interface.
  These two interfaces are now managed via cdev structures.

* Numerous minor cleanups
Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/iio/Kconfig

@@ -11,6 +11,12 @@ menuconfig IIO
 	  Documentation/industrialio for more information.
 if IIO
 
+config IIO_RING_BUFFER
+	bool "Enable ring buffer support within IIO"
+	help
+	  Provide core support for various ring buffer based data
+	  acquisition methods.
+
 source "drivers/staging/iio/accel/Kconfig"
 source "drivers/staging/iio/adc/Kconfig"
 source "drivers/staging/iio/light/Kconfig"

drivers/staging/iio/Makefile

@@ -4,6 +4,7 @@
 
 obj-$(CONFIG_IIO) += industrialio.o
 industrialio-y := industrialio-core.o
+industrialio-$(CONFIG_IIO_RING_BUFFER) += industrialio-ring.o
 
 obj-y += accel/
 obj-y += adc/