xen: arm: Use generic mem{cpy, move, set, zero} on 64-bit

No optimised versions are available in Linux yet (meaning I couldn't
copy them).

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Tim Deegan <tim@xen.org>

xen/include/asm-arm/string.h

@@ -3,6 +3,7 @@
 
 #include <xen/config.h>
 
+#if defined(CONFIG_ARM_32)
 #define __HAVE_ARCH_MEMCPY
 extern void * memcpy(void *, const void *, __kernel_size_t);
 
@@ -27,6 +28,8 @@ extern void __memzero(void *ptr, __kernel_size_t n);
                 (__p);                                                  \
         })
 
+#endif
+
 #endif /* __ARM_STRING_H__ */
 /*
  * Local variables: