[IA64] fixes configs and add default config for ia64 xen domU

This patch fixes xen related Kconfigs and add default config
file for ia64 xen domU.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Tony Luck <aegl@agluck-desktop.(none)>
diff --git a/arch/ia64/Kconfig b/arch/ia64/Kconfig
index 20d6d28..4eb45c0 100644
--- a/arch/ia64/Kconfig
+++ b/arch/ia64/Kconfig
@@ -221,7 +221,11 @@
 
 config IA64_XEN_GUEST
 	bool "Xen guest"
+	select SWIOTLB
 	depends on XEN
+	help
+	  Build a kernel that runs on Xen guest domain. At this moment only
+	  16KB page size in supported.
 
 endchoice