stm32/usb: Add "port" keyword argument to pyb.usb_mode, to select FS/HS.
stm32/usb: Add "port" keyword argument to pyb.usb_mode, to select FS/HS.

If the board supports it, the USB port can now be explicitly specified, eg:

    pyb.usb_mode('VCP', port=0).

port=0 is USB FS and port=1 is USB HS.

henriknelson/micropython,pozetroninc/micropython,pozetroninc/micropython,pfalcon/micropython,kerneltask/micropython,adafruit/circuitpython,pozetroninc/micropython,kerneltask/micropython,bvernoux/micropython,pfalcon/micropython,pramasoul/micropython,tobbad/micropython,henriknelson/micropython,adafruit/circuitpython,selste/micropython,pramasoul/micropython,tobbad/micropython,pfalcon/micropython,MrSurly/micropython,bvernoux/micropython,henriknelson/micropython,trezor/micropython,selste/micropython,MrSurly/micropython,selste/micropython,trezor/micropython,selste/micropython,bvernoux/micropython,adafruit/circuitpython,pfalcon/micropython,tobbad/micropython,bvernoux/micropython,adafruit/circuitpython,pozetroninc/micropython,henriknelson/micropython,pramasoul/micropython,MrSurly/micropython,trezor/micropython,adafruit/circuitpython,pramasoul/micropython,bvernoux/micropython,pfalcon/micropython,kerneltask/micropython,trezor/micropython,pramasoul/micropython,trezor/micropython,pozetroninc/micropython,kerneltask/micropython,adafruit/circuitpython,selste/micropython,MrSurly/micropython,henriknelson/micropython,kerneltask/micropython,MrSurly/micropython,tobbad/micropython,tobbad/micropython