[stm32] Usb tunnel

- add usb_tunnel for stm32
- replace usb_tunnel_0 and usb_tunnel_1 targets on lpc with one usb_tunnel that is configurable
- cleanup setup makefile
- rename VCOM_transmit_message to VCOM_send_message
- check if usb is connected in putchar and send_message

Open questions/todo:
- [ ] use one usb_tunnel for both stm32 and lpc (only functional difference is currently the minimum blink time on lpc)
- [ ] really keep the setup firmware? Or just put the few targets we have there also in test_progs?