This fixes the build for some esp32 and nrf boards (for example
`ARDUINO_NANO_33_BLE_SENSE` and `ARDUINO_NANO_ESP32`) due to commit
c98789a6d8e05acb608afe4b30cf3ca563419b2d. Changes are:
- Allow the CDC TX/RX functions in `mp_usbd_cdc.c` to be enabled
separately to those needed for `MICROPY_HW_USB_CDC_1200BPS_TOUCH`.
- Add `MICROPY_EXCLUDE_SHARED_TINYUSB_USBD_CDC` option as a temporary
workaround for the nrf port to use.
- Declare `mp_usbd_line_state_cb()` in a header as a public function.
- Fix warning with type cast of `.callback_line_state_changed`.
Signed-off-by: Damien George <damien@micropython.org>
84a8f7ea6d