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>
diff --git a/include/linux/iio/configfs.h b/include/linux/iio/configfs.h
new file mode 100644
index 0000000..93befd6
--- /dev/null
+++ b/include/linux/iio/configfs.h
@@ -0,0 +1,15 @@
+/*
+ * 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 */