nk3: Use mboot instead of spsdk for bootloader

[robin-nitrokey]

With this patch, we use mboot instead of spsdk for bootloader
communication. This speeds up the process noticably on Linux and by
several orders of magnitude on Windows.

---

Currently, basic communication works but the update fails with this error:

  File "/home/robin/reps/pynitrokey/venv/lib/python3.9/site-packages/pynitrokey/nk3/bootloader.py", line 92, in list                                                                                               
    for device in RawHid.enumerate(VID_NITROKEY, PID_NITROKEY3_BOOTLOADER):                              
  File "/home/robin/reps/pynitrokey/venv/lib/python3.9/site-packages/mboot/connection/usb.py", line 337, in enumerate                                                                                              
    config = dev.get_active_configuration()                                                              
  File "/home/robin/reps/pynitrokey/venv/lib/python3.9/site-packages/usb/core.py", line 875, in get_active_configuration                                                                                           
    return self._ctx.get_active_configuration(self)                                                      
  File "/home/robin/reps/pynitrokey/venv/lib/python3.9/site-packages/usb/core.py", line 102, in wrapper
    return f(self, *args, **kwargs)                                                                      
  File "/home/robin/reps/pynitrokey/venv/lib/python3.9/site-packages/usb/core.py", line 236, in get_active_configuration                                                                                           
    self.managed_open()  
  File "/home/robin/reps/pynitrokey/venv/lib/python3.9/site-packages/usb/core.py", line 102, in wrapper  
    return f(self, *args, **kwargs)                                                                      
  File "/home/robin/reps/pynitrokey/venv/lib/python3.9/site-packages/usb/core.py", line 120, in managed_open
    self.handle = self.backend.open_device(self.dev)                                                                                                                                                               
  File "/home/robin/reps/pynitrokey/venv/lib/python3.9/site-packages/usb/backend/libusb1.py", line 786, in open_device                                                                                             
    return _DeviceHandle(dev)                                                                            
  File "/home/robin/reps/pynitrokey/venv/lib/python3.9/site-packages/usb/backend/libusb1.py", line 643, in __init__                                                                                                
    _check(_lib.libusb_open(self.devid, byref(self.handle)))         
  File "/home/robin/reps/pynitrokey/venv/lib/python3.9/site-packages/usb/backend/libusb1.py", line 595, in _check                                                                                                  
    raise USBError(_strerror(ret), ret, _libusb_errno[ret])                                              
usb.core.USBError: [Errno 13] Access denied (insufficient permissions)

[robin-nitrokey]

The speed issue with spsdk has been fixed so we no longer need this.