lib: Include helper libc functions directly in libsbi.

libsbi needs some of the custom libc functions. It should be directly
included in libsbi instead of platform specific libraries.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Acked-by: Anup Patel <anup.patel@wdc.com>

include/sbi/string.h

@@ -0,0 +1,39 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2019 Western Digital Corporation or its affiliates.
+ *
+ * Authors:
+ *   Atish Patra <atish.patra@wdc.com>
+ */
+
+#ifndef __STRING_H__
+#define __STRING_H__
+
+#include <sbi/sbi_types.h>
+
+int strcmp(const char *a, const char *b);
+
+size_t strlen(const char *str);
+
+size_t strnlen(const char *str, size_t count);
+
+char *strcpy(char *dest, const char *src);
+
+char *strncpy(char *dest, const char *src, size_t count);
+
+char *strchr(const char *s, int c);
+
+char *strrchr(const char *s, int c);
+
+void *memset(void *s, int c, size_t count);
+
+void *memcpy(void *dest, const void *src, size_t count);
+
+void *memmove(void *dest, const void *src, size_t count);
+
+int memcmp(const void *s1, const void *s2, size_t count);
+
+void *memchr(const void *s, int c, size_t count);
+
+#endif