bdi: add helper function for doing init and register of a bdi for a file system

Pretty trivial helper, just sets up the bdi and registers it. An atomic
sequence count is used to ensure that the registered sysfs names are
unique.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index fcbc26a..e19c677 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -101,6 +101,7 @@
 		const char *fmt, ...);
 int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
 void bdi_unregister(struct backing_dev_info *bdi);
+int bdi_setup_and_register(struct backing_dev_info *, char *, unsigned int);
 void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
 				long nr_pages);
 int bdi_writeback_task(struct bdi_writeback *wb);