stm32/spi: Factor out code to calculate SPI source frequency.
stm32/spi: Factor out code to calculate SPI source frequency.

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