block: fix q->blkg_list corruption during disk rebind

In the Linux kernel, the following vulnerability has been resolved:

block: fix q->blkg_list corruption during disk rebind

Multiple gendisk instances can allocated/added for single request queue

in case of disk rebind. blkg may still stay in q->blkg_list when calling

blkcg_init_disk() for rebind, then q->blkg_list becomes corrupted.

Fix the list corruption issue by:

- add blkg_init_queue() to initialize q->blkg_list & q->blkcg_mutex only

- move calling blkg_init_queue() into blk_alloc_queue()

The list corruption should be started since commit f1c006f1c685 ("blk-cgroup:

synchronize pd_free_fn() from blkg_free_workfn() and blkcg_deactivate_policy()")

which delays removing blkg from q->blkg_list into blkg_free_workfn().