LoongArch: Remove clock setting during cpu hotplug stage

mainline inclusion
from mainline-v5.19
commit 71610ab1
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5OHOB


CVE: NA

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

On physical machine we can save power by disabling clock of hot removed
cpu. However as different platforms require different methods to
configure clocks, the code is platform-specific, and probably belongs to
firmware/pmu or cpu regulator, rather than generic arch/loongarch code.

Also, there is no such register on QEMU virt machine since the
clock/frequency regulation is not emulated.

This patch removes the hard-coded clock register accesses in generic
LoongArch cpu hotplug flow.

Reviewed-by: WANG Xuerui <git@xen0n.name>
Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>