iio:configfs: Introduce iio/configfs.h to provide a location for the configfs_subsystem

This exported element needs to be accesible to all drivers using configfs
within IIO.  Previously it was in the sw_trig.h file which only convered one
such usecase.  This also fixes a sparse warning as it is now in a header
that makes sense to include from industrialio-configfs.c

Signed-off-by: Jonathan Cameron < jic23@kernel.org>

drivers/iio/industrialio-configfs.c

@@ -15,6 +15,7 @@
 #include <linux/slab.h>
 
 #include <linux/iio/iio.h>
+#include <linux/iio/configfs.h>
 
 static struct config_item_type iio_root_group_type = {
 	.ct_owner       = THIS_MODULE,

drivers/iio/industrialio-sw-trigger.c

@@ -15,6 +15,7 @@
 #include <linux/slab.h>
 
 #include <linux/iio/sw_trigger.h>
+#include <linux/iio/configfs.h>
 #include <linux/configfs.h>
 
 static struct config_group *iio_triggers_group;

include/linux/iio/configfs.h

+/*
+ * Industrial I/O configfs support
+ *
+ * Copyright (c) 2015 Intel Corporation
+ *
+ * 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.
+ */
+#ifndef __IIO_CONFIGFS
+#define __IIO_CONFIGFS
+
+extern struct configfs_subsystem iio_configfs_subsys;
+
+#endif /* __IIO_CONFIGFS */

include/linux/iio/sw_trigger.h

@@ -20,7 +20,6 @@
 	module_driver(__iio_sw_trigger_type, iio_register_sw_trigger_type, \
 		      iio_unregister_sw_trigger_type)
 
-extern struct configfs_subsystem iio_configfs_subsys;
 struct iio_sw_trigger_ops;
 
 struct iio_sw_trigger_type {