kvm: arm64: fix some pvsched bugs

virt inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6E2VI



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1. Clear kvm_vcpu_arch::pvsched::base on vcpu reset
The guest memory will otherwise be corrupted by KVM if we reboot into
an old guest kernel which is **not** aware of the pvsched feature.

2. Fix boot cpu pvsched init abnormal
The pv_sched_init was called too early in the boot in setup_arch, hence
pvsched_vcpu_state was not initializedfo vcpu 0.

Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: yezengruan <yezengruan@huawei.com>