iio: Move callback buffer to its own module

Currently the IIO callback buffer implementation is directly built into the
IIO core module when enabled. Given that the callback buffer module is
standalone functionallity there is really no reason to do this. So move it
to its own module.

Also rename the source to follow the standard IIO module naming convention
as well as add a license notice to the file.

Signed-off-by: Lars-Peter Clausen <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/Kconfig

···
 if IIO_BUFFER
 
 config IIO_BUFFER_CB
-	bool "IIO callback buffer used for push in-kernel interfaces"
+	tristate "IIO callback buffer used for push in-kernel interfaces"
 	help
 	  Should be selected by any drivers that do in-kernel push
 	  usage.  That is, those where the data is pushed to the consumer.

drivers/iio/Makefile

···
 industrialio-y := industrialio-core.o industrialio-event.o inkern.o
 industrialio-$(CONFIG_IIO_BUFFER) += industrialio-buffer.o
 industrialio-$(CONFIG_IIO_TRIGGER) += industrialio-trigger.o
-industrialio-$(CONFIG_IIO_BUFFER_CB) += buffer_cb.o
 
+obj-$(CONFIG_IIO_BUFFER_CB) += industrialio-buffer-cb.o
 obj-$(CONFIG_IIO_TRIGGERED_BUFFER) += industrialio-triggered-buffer.o
 obj-$(CONFIG_IIO_KFIFO_BUF) += kfifo_buf.o
 

drivers/iio/buffer_cb.c drivers/iio/industrialio-buffer-cb.c

···
+/* The industrial I/O callback buffer
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published by
+ * the Free Software Foundation.
+ */
+
 #include <linux/kernel.h>
+#include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/err.h>
 #include <linux/export.h>
···
 	return cb_buffer->channels;
 }
 EXPORT_SYMBOL_GPL(iio_channel_cb_get_channels);
+
+MODULE_AUTHOR("Jonathan Cameron <[e-mail]>");
+MODULE_DESCRIPTION("Industrial I/O callback buffer");
+MODULE_LICENSE("GPL");