stm32/system_stm32f0: Enable PWR clock on startup.
stm32/system_stm32f0: Enable PWR clock on startup.

To be consistent with how F4/F7/H7/L4 works in system_stm32.c.  The power
control peripheral is needed at least for the RTC.

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