This patch removes the redundant throttle code that was present in
block and fsdev device files. Now the common code is moved
to a single file.

Signed-off-by: Pradeep Jagadeesh <pradeep.jagadeesh@huawei.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
(fix indent nit, Greg Kurz)
Signed-off-by: Greg Kurz <groug@kaod.org>