LU-15420 libcfs: replace deprecated CPU-hotplug functions

LU-15420 libcfs: replace deprecated CPU-hotplug functions

Kernel 5.15 commit 8c854303ce0e38e5bbedd725ff39da7e235865d8
removed deprecated CPU-hotplug functions get_online_cpus()
and put_online_cpus(). They map directly to cpus_read_lock()
and cpus_read_unlock().

Change-Id: I09d489cd3ca9a575b20ea25f24210702fbfdd725
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/46085
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: Maloo <maloo@whamcloud.com>