stm32/modmachine: Get machine.sleep working on L4 MCUs.
stm32/modmachine: Get machine.sleep working on L4 MCUs.

When waking from stop mode most of the system is still in the same state as
before entering stop, so only minimal configuration is needed to bring the
system clock back online.

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