[RESEND PATCH v2 3/3] block: hide back blk_freeze_queue_start and export its blk-mq alias

[Jinlong Chen]

> > I agree that the freezing stuff (maybe also the quiescing stuff) should
> > move out of the mq namespace. If now is not the proper time, I'll leave
> > them alone. I'll resend patch 1 alone without the comment.
> 
> The quiesce actually is entirely blk-mq specific, which just have some
> careless callers.

Got it, thank you!

Thanks!
Jinlong Chen