blkio: Export some symbols from blkio as its user CFQ can be a module

o blkio controller is inside the kernel and cfq makes use of interfaces
  exported by blkio. CFQ can be a module too, hence export symbols used
  by CFQ.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --cc block/blk-cgroup.c
Simple merge

diff --cc block/blk-cgroup.h
Simple merge

diff --cc block/cfq-iosched.c
Simple merge