Add support for resetting RP2040 via the USB connection when using pico_stdio_usb

- setting baud rate to magic value (default=1200) will cause a reset to BOOTSEL mode
	- a VENDOR interface along side the CDC interface can be used to reset via refular flash boot, or into
	  BOOTSEL mode with control for the reset_usb_boot parameters for the latter
either method can be configured/enabled/disabled via #define

src/rp2_common/pico_stdio_usb/CMakeLists.txt

@@ -4,6 +4,7 @@ if (TARGET tinyusb_device_unmarked)
     target_include_directories(pico_stdio_usb INTERFACE ${CMAKE_CURRENT_LIST_DIR}/include)
 
     target_sources(pico_stdio_usb INTERFACE
+        ${CMAKE_CURRENT_LIST_DIR}/reset_interface.c
         ${CMAKE_CURRENT_LIST_DIR}/stdio_usb.c
         ${CMAKE_CURRENT_LIST_DIR}/stdio_usb_descriptors.c
     )