intel_iommu: support all masks in interrupt entry cache invalidation

Linux guests do not gracefully handle cases when the invalidation mask
they wanted is not supported, probably because real hardware always
allowed all.

We can just say that all 16 masks are supported, because both
ioapic_iec_notifier and kvm_update_msi_routes_all invalidate all caches.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
