shared/tinyusb: Avoid symbol clash on targets with external TinyUSB.

On targets that provide a reference TinyUSB implementation, like ESP32,
the SDK already defines and implements standard callback functions such
as tud_cdc_line_state_cb(). This causes a symbol clash when enabling
shared implementations like the MicroPython 1200 touch functionality.

To avoid this symbol clash, add an optional macro to allow ports to
use a different function name in the shared implementation.
Signed-off-by: NLuca Burelli <l.burelli@arduino.cc>

shared/tinyusb/mp_cdc_common.c

@@ -39,7 +39,13 @@ STATIC void usbd_cdc_run_bootloader_task(mp_sched_node_t *node) {
     machine_bootloader(0, NULL);
 }
 
-void tud_cdc_line_state_cb(uint8_t itf, bool dtr, bool rts) {
+void
+#if MICROPY_HW_USB_EXTERNAL_TINYUSB
+mp_usbd_line_state_cb
+#else
+tud_cdc_line_state_cb
+#endif
+    (uint8_t itf, bool dtr, bool rts) {
     if (dtr == false && rts == false) {
         // Device is disconnected.
         cdc_line_coding_t line_coding;