nds32: Library functions

This patch add support for various library functions.

Signed-off-by: Vincent Chen <vincentc@andestech.com>
Signed-off-by: Greentime Hu <greentime@andestech.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>

arch/nds32/include/asm/swab.h

@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2005-2017 Andes Technology Corporation
+
+#ifndef __NDS32_SWAB_H__
+#define __NDS32_SWAB_H__
+
+#include <linux/types.h>
+#include <linux/compiler.h>
+
+static __inline__ __attribute_const__ __u32 ___arch__swab32(__u32 x)
+{
+	__asm__("wsbh   %0, %0\n\t"	/* word swap byte within halfword */
+		"rotri  %0, %0, #16\n"
+		:"=r"(x)
+		:"0"(x));
+	return x;
+}
+
+static __inline__ __attribute_const__ __u16 ___arch__swab16(__u16 x)
+{
+	__asm__("wsbh   %0, %0\n"	/* word swap byte within halfword */
+		:"=r"(x)
+		:"0"(x));
+	return x;
+}
+
+#define __arch_swab32(x) ___arch__swab32(x)
+#define __arch_swab16(x) ___arch__swab16(x)
+
+#if !defined(__STRICT_ANSI__) || defined(__KERNEL__)
+#define __BYTEORDER_HAS_U64__
+#define __SWAB_64_THRU_32__
+#endif
+
+#endif /* __NDS32_SWAB_H__ */