stm32/rtc: Allow overriding startup timeouts from mpconfigboard.
stm32/rtc: Allow overriding startup timeouts from mpconfigboard.

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