Add an implementation for the memchr library function

Change-Id: Icded479d246f7cce8a3d2154c69f75178fa513e1
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: http://review.coreboot.org/708
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Mathias Krause <minipli@googlemail.com>

src/lib/memchr.c

@@ -0,0 +1,11 @@
+#include <string.h>
+void *memchr(const void *s, int c, size_t n)
+{
+	const unsigned char *sc = s;
+	while (n--) {
+		if (*sc == (unsigned char)c)
+			return (void *)sc;
+		sc++;
+	}
+	return NULL;
+}