KVM: x86: Warning APICv inconsistency only when vcpu APIC mode is valid

When launching a VM with x2APIC and specify more than 255 vCPUs,
the guest kernel can disable x2APIC (e.g. specify nox2apic kernel option).
The VM fallbacks to xAPIC mode, and disable the vCPU ID 255 and greater.

In this case, APICV is deactivated for the disabled vCPUs.
However, the current APICv consistency warning does not account for
this case, which results in a warning.

Therefore, modify warning logic to report only when vCPU APIC mode
is valid.

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Message-Id: <20220519102709.24125-15-suravee.suthikulpanit@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>