blk-throttle: enable hierarchical throttle in cgroup v1

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8QYR1


CVE: NA

-----------------------------------------------

blkio subsytem is not under default hierarchy in cgroup v1 by default,
which means configurations will only be effective on current cgroup
for io throttle.

This patch introduces a new feature that enable default hierarchy for
io throttle, which means configurations will be effective on child cgroups.
Such feature is disabled by default, and can be enabled by:

1) set CONFIG_BLK_DEV_SUPPORT_LEGACY_GLOBAL_LIMIT, then
2) adding "blkcg_global_limit=1" or "blkcg_global_limit=Y" or
"blkcg_global_limit=y" in boot cmd;

Signed-off-by: Yu Kuai <yukuai3@huawei.com>