VT-d posted interrupt is relying on the CPU side's posted interrupt.
Need to check whether VCPU's APICv is active before enabing VT-d
posted interrupt.

Fixes: d62caabb
Cc: stable@vger.kernel.org
Signed-off-by: NYang Zhang <yang.zhang.wz@gmail.com>
Signed-off-by: NShengge Ding <shengge.dsg@alibaba-inc.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>