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 < [email protected]>

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;