LoongArch: KVM: fix vcpu timer functions

LoongArch inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7QJIN



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Fix vcpu timer initialize, saved, restore and triggered functions.
As the previous code does not init vcpu timer, and the timer value
should add time value instead of ticks value to calculate the expire
time when vcpu timer triggered.

Signed-off-by: Tianrui Zhao <zhaotianrui@loongson.cn>