usb_serial_jtag: support usb_serial_jtag on esp32c3

USB serial/jtag controller: Add vfs (logging/printf), panic handler, gdb support.

See merge request espressif/esp-idf!12925

components/esp_gdbstub/private_include/esp_gdbstub_common.h

@@ -119,6 +119,11 @@ void esp_gdbstub_putchar(int c);
  */
 int esp_gdbstub_readmem(intptr_t addr);
 
+/**
+ * Make sure all bytes sent using putchar() end up at the host.
+ * (Usually stubbed for UART, but can be useful for other channels)
+ */
+void esp_gdbstub_flush(void);
 
 /**** GDB packet related functions ****/