First of all, vtd_setup_msi() is provided. It setup IRTE entries,
meanwhile, setup PCI device MSI vectors corresponding to VT-d spec.

Meanwhile, IR MSI test is added to intel IOMMU unit test. The basic IR
test is carried out by a edu INTR raise request. When write to the intr
raise register, interrupt will be generated. Type of interrupt will
depend on the setup (either INTx or MSI).

Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>