A board can now name the CDC ports, eg:
#define MICROPY_HW_USB_CDC_NUM (3)
#define MICROPY_HW_USB_INTERFACE_CDC0_STRING "REPL"
#define MICROPY_HW_USB_INTERFACE_CDC1_STRING "GDB Server"
#define MICROPY_HW_USB_INTERFACE_CDC2_STRING "UART Port"
Signed-off-by: Damien George <damien@micropython.org>