stm32/main: Run optional frozen module at boot.
stm32/main: Run optional frozen module at boot.

If a board specifies a filename via MICROPY_BOARD_FROZEN_BOOT_FILE then
that will be run on start up, before the usual boot.py.

adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython