xfs: rename block gc start and stop functions

mainline-inclusion
from mainline-v5.11-rc4
commit c9a6526f
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4KIAO
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c9a6526fe7ae64528d924c6f255af15312211432



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

Shorten the names of the two functions that start and stop block
preallocation garbage collection and move them up to the other blockgc
functions.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Lihong Kou <koulihong@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>