blkio: Allow CFQ group IO scheduling even when CFQ is a module

o Now issues of blkio controller and CFQ in module mode should be fixed.
  Enable the cfq group scheduling support in module mode.

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