Add support for ARM64 architecture

This patch adds aarch64 as a supported architecture to the configure script.

Signed-off-by: Joao Pinto <jpinto@synopsys.com>
---

--- b/configure	2015-09-15 17:30:46.187307557 +0100
+++ a/configure	2015-09-15 17:31:11.729307537 +0100
@@ -2496,6 +2496,10 @@
     arch='arc'
     iproc='arc'
     ;;
+  aarch64)
+    arch='arm64'
+    iproc='arm64'
+    ;;
 
   *)
     echo "The architecture of your CPU ($host_arch) is not supported by this configure script"