x86/kvm: Don't waste kvmclock memory if there is nopv parameter

When the "nopv" command line parameter is used, it should not waste
memory for kvmclock.

Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <1646727529-11774-1-git-send-email-wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>