sw64: track last vpn in struct cpuinfo_sw64

Sunway inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I645MA



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The sw64_kvm_last_vpn[] suffers from false sharing, so remove
it and track last vpn in struct cpuinfo_sw64.

Signed-off-by: He Sheng <hesheng@wxiat.com>
Reviewed-by: Cui Wei <cuiwei@wxiat.com>
Signed-off-by: Gu Zitao <guzitao@wxiat.com>