usbd: Add USB device drivers implemented in Python.

Rely on support implemented in the machine.USBD() object on the MicroPython
side, providing a thin wrapper around TinyUSB "application" device class
driver.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

Author: projectgus

micropython/usbd/__init__.py

@@ -0,0 +1,4 @@
+from .device import get_usbdevice, USBInterface
+from .hid import HIDInterface, MouseInterface
+from .midi import DummyAudioInterface, MIDIInterface, MidiUSB
+from . import utils