hw/i386/x86-iommu: Add missing stubs

In commit 6c730e4af9 we introduced a stub to build the MicroVM
machine without Intel IOMMU. This stub is incomplete for the
other PC machines. Add the missing stubs.

Fixes: 6c730e4af9 ("pc: stubify x86 iommu", 2019-12-17)
Reported-by: Travis-CI
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20191220154225.25879-1-philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/i386/x86-iommu-stub.c

@@ -32,3 +32,12 @@ X86IOMMUState *x86_iommu_get_default(void)
     return NULL;
 }
 
+bool x86_iommu_ir_supported(X86IOMMUState *s)
+{
+    return false;
+}
+
+IommuType x86_iommu_get_type(void)
+{
+    abort();
+}