[IA64] enable setting DMAR on by default

The previous commit which introduced the DMAR_DEFAULT_ON setting in
drivers/pci/dmar.c neglected to add the ability for ia64 to enable
the IOMMU by default. Rectify that mistake, doh!
Signed-off-by: Kyle McMartin <kyle@redhat.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/Kconfig

@@ -638,6 +638,17 @@ config DMAR
 	  and include PCI device scope covered by these DMA
 	  remapping devices.
 
+config DMAR_DEFAULT_ON
+	def_bool y
+	prompt "Enable DMA Remapping Devices by default"
+	depends on DMAR
+	help
+	  Selecting this option will enable a DMAR device at boot time if
+	  one is found. If this option is not selected, DMAR support can
+	  be enabled by passing intel_iommu=on to the kernel. It is
+	  recommended you say N here while the DMAR code remains
+	  experimental.
+
 endmenu
 
 endif