smp: add set_nr_cpu_ids()

mainline inclusion
from mainline-v6.1-rc1
commit 38bef8e5
category: cleanup
bugzilla: https://gitee.com/openeuler/kernel/issues/I8KQBZ
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=38bef8e57f2149acd2c910a98f57dd6291d2e0ec



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

In preparation to support compile-time nr_cpu_ids, add a setter for
the variable.

This is a no-op for all arches.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Zheng Zucheng <zhengzucheng@huawei.com>