KVM: x86: Check for in-kernel xAPIC when querying APICv for directed yield

Use kvm_vcpu_apicv_active() to check if APICv is active when seeing if a
vCPU is a candidate for directed yield due to a pending ACPIv interrupt.
This will allow moving apicv_active into kvm_lapic without introducing a
potential NULL pointer deref (kvm_vcpu_apicv_active() effectively adds a
pre-check on the vCPU having an in-kernel APIC).

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220614230548.3852141-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>