sw64: kvm: fix guest longtime offset of VCPU

Sunway inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I645O8



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Other VCPUs have to sync longtime offset with VCPU0 to ensure
the consistency of clock source, and this will avoid RCU CPU
stalls in guest live migration.

Signed-off-by: Min Fanlei <minfanlei@wxiat.com>
Reviewed-by: He Sheng <hesheng@wxiat.com>
Signed-off-by: Gu Zitao <guzitao@wxiat.com>