Blackfin: enable atomic64_t support

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/arch/blackfin/include/asm/atomic.h b/arch/blackfin/include/asm/atomic.h
index d27c627..e485089 100644
--- a/arch/blackfin/include/asm/atomic.h
+++ b/arch/blackfin/include/asm/atomic.h
@@ -121,4 +121,6 @@
 
 #endif
 
+#include <asm-generic/atomic64.h>
+
 #endif