sandbox: Add serial test

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

include/common.h

@@ -359,6 +359,7 @@ void	serial_putc_raw(const char);
 void	serial_puts   (const char *);
 int	serial_getc   (void);
 int	serial_tstc   (void);
+int	serial_setconfig(uint config);
 
 /* $(CPU)/speed.c */
 int	get_clocks (void);