csky: Library functions

This patch adds string optimize codes and some auxiliary codes.

Signed-off-by: Chen Linfei <linfei_chen@c-sky.com>
Signed-off-by: Mao Han <han_mao@c-sky.com>
Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>

arch/csky/include/asm/string.h

@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+// Copyright (C) 2018 Hangzhou C-SKY Microsystems co.,ltd.
+
+#ifndef _CSKY_STRING_MM_H_
+#define _CSKY_STRING_MM_H_
+
+#ifndef __ASSEMBLY__
+#include <linux/types.h>
+#include <linux/compiler.h>
+#include <abi/string.h>
+#endif
+
+#endif /* _CSKY_STRING_MM_H_ */