iommu/vt-d: Make intr-remapping initialization generic

This patch introduces irq_remap_ops to hold implementation
specific function pointer to handle interrupt remapping. As
the first part the initialization functions for VT-d are
converted to these ops.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
diff --git a/arch/ia64/include/asm/intr_remapping.h b/arch/ia64/include/asm/intr_remapping.h
new file mode 100644
index 0000000..095aa0d
--- /dev/null
+++ b/arch/ia64/include/asm/intr_remapping.h
@@ -0,0 +1,4 @@
+#ifndef __IA64_INTR_REMAPPING_H
+#define __IA64_INTR_REMAPPING_H
+#define intr_remapping_enabled 0
+#endif