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/abiv1/memset.c

@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2018 Hangzhou C-SKY Microsystems co.,ltd.
+
+#include <linux/types.h>
+
+void *memset(void *dest, int c, size_t l)
+{
+	char *d = dest;
+	int ch = c & 0xff;
+	int tmp = (ch | ch << 8 | ch << 16 | ch << 24);
+
+	while (((uintptr_t)d & 0x3) && l--)
+		*d++ = ch;
+
+	while (l >= 16) {
+		*(((u32 *)d))   = tmp;
+		*(((u32 *)d)+1) = tmp;
+		*(((u32 *)d)+2) = tmp;
+		*(((u32 *)d)+3) = tmp;
+		l -= 16;
+		d += 16;
+	}
+
+	while (l > 3) {
+		*(((u32 *)d)) = tmp;
+		l -= 4;
+		d += 4;
+	}
+
+	while (l) {
+		*d = ch;
+		l--;
+		d++;
+	}
+
+	return dest;
+}