stm32/modbluetooth_hci: Use a static mp_irq_obj_t for BT HCI UART IRQ.
stm32/modbluetooth_hci: Use a static mp_irq_obj_t for BT HCI UART IRQ.

So that the IRQ handler does not need to be traced by the GC.

adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,henriknelson/micropython,henriknelson/micropython,henriknelson/micropython,pramasoul/micropython,MrSurly/micropython,henriknelson/micropython,bvernoux/micropython,bvernoux/micropython,MrSurly/micropython,pramasoul/micropython,bvernoux/micropython,pramasoul/micropython,MrSurly/micropython,pramasoul/micropython,MrSurly/micropython,adafruit/circuitpython,bvernoux/micropython,MrSurly/micropython,adafruit/circuitpython,adafruit/circuitpython,pramasoul/micropython,bvernoux/micropython,henriknelson/micropython