KVM: ia64: define kvm_lapic_enabled() to fix a compile error

The following patch

  commit 57ce1659316f4ca298919649f9b1b55862ac3826
  KVM: x86: In DM_LOWEST, only deliver interrupts to vcpus with enabled LAPIC's

ignored the fact that kvm_irq_delivery_to_apic() was also used by ia64.

We define kvm_lapic_enabled() to fix a compile error caused by this.
This will have the same effect as reverting the problematic patch for ia64.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Avi Kivity <avi@redhat.com>