iio: core: Implement devm_iio_device_{register,unregister}

Add device managed devm_iio_device_{register,unregister}()
to automatically unregister IIO drivers thus leading to
simplified IIO driver code.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Tested-by: Lars-Peter Clausen <lars@metafoo.de>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
index 256a90a..a8cabda 100644
--- a/include/linux/iio/iio.h
+++ b/include/linux/iio/iio.h
@@ -510,6 +510,9 @@
  **/
 void iio_device_unregister(struct iio_dev *indio_dev);
 
+int devm_iio_device_register(struct device *dev, struct iio_dev *indio_dev);
+void devm_iio_device_unregister(struct device *dev, struct iio_dev *indio_dev);
+
 /**
  * iio_push_event() - try to add event to the list for userspace reading
  * @indio_dev:		IIO device structure