liburcu: recognize aarch64_be for hierofalcon 5.0 release

Make the same as "aarch64" internally.

Signed-off-by: alexandru.vaduva@enea.com

diff -Naur a/configure.ac b/configure.ac
--- a/configure.ac	2015-08-14 15:50:56.267058228 +0200
+++ b/configure.ac	2015-08-14 15:50:27.140296920 +0200
@@ -80,6 +80,7 @@
 	[mips*], [ARCHTYPE="mips"],
 	[tile*], [ARCHTYPE="gcc"],
 	[aarch64], [ARCHTYPE="gcc"],
+	[aarch64_be], [ARCHTYPE="gcc"],
 	[ARCHTYPE="unknown"]
 )