blkcg: misc preparations for unified hierarchy interface

* Export blkg_dev_name()

* Drop unnecessary @cft from __cfq_set_weight().

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@fb.com>
(cherry picked from commit dd165eb3bb4ef16bcdb75417add40633f38c52b8)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
3 files changed