libc: Import from TF-A

Based on arm-trusted-firware commit 873e394b3bf93214a441f9f98237b58fbbea55aa

Change-Id: I510e092f2b9ff333e9461bdde8d80ed1fab1460c
Signed-off-by: Ambroise Vincent <ambroise.vincent@arm.com>
diff --git a/lib/libc/memchr.c b/lib/libc/memchr.c
new file mode 100644
index 0000000..2eba47c
--- /dev/null
+++ b/lib/libc/memchr.c
@@ -0,0 +1,20 @@
+/*
+ * Copyright (c) 2013-2018, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stddef.h>
+
+void *memchr(const void *src, int c, size_t len)
+{
+	const char *s = src;
+
+	while (len--) {
+		if (*s == c)
+			return (void *) s;
+		s++;
+	}
+
+	return NULL;
+}