nds32: System calls handling

This patch adds support for system calls.

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

arch/nds32/include/uapi/asm/unistd.h

@@ -0,0 +1,11 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2005-2017 Andes Technology Corporation
+
+#define __ARCH_WANT_SYNC_FILE_RANGE2
+
+/* Use the standard ABI for syscalls */
+#include <asm-generic/unistd.h>
+
+/* Additional NDS32 specific syscalls. */
+#define __NR_cacheflush		(__NR_arch_specific_syscall)
+__SYSCALL(__NR_cacheflush, sys_cacheflush)