xfs: expose the blockgc workqueue knobs publicly

mainline-inclusion
from mainline-v5.11-rc4
commit 47bd6d34
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=47bd6d3457fb96d287278027aed8a78d14f1d32d



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Expose the workqueue sysfs knobs for the speculative preallocation gc
workers on all kernels, and update the sysadmin information.

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>