lib: string: Implement strlcat

This introduces strlcat, which provides a safer interface than strncat. It
never copies more than its size bytes, including the terminating nul. In
addition, it never reads past dest[size - 1], even if dest is not
nul-terminated.

This also removes the stub for dwc3 now that we have a proper
implementation.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

include/linux/string.h

@@ -35,6 +35,9 @@ extern char * strcat(char *, const char *);
 #ifndef __HAVE_ARCH_STRNCAT
 extern char * strncat(char *, const char *, __kernel_size_t);
 #endif
+#ifndef __HAVE_ARCH_STRLCAT
+size_t strlcat(char *, const char *, size_t);
+#endif
 #ifndef __HAVE_ARCH_STRCMP
 extern int strcmp(const char *,const char *);
 #endif