stm32/spi: Add support for a board naming SPI peripherals 4, 5 and 6.
stm32/spi: Add support for a board naming SPI peripherals 4, 5 and 6.

bvernoux/micropython,henriknelson/micropython,trezor/micropython,adafruit/circuitpython,adafruit/micropython,ryannathans/micropython,bvernoux/micropython,pozetroninc/micropython,kerneltask/micropython,adafruit/micropython,kerneltask/micropython,selste/micropython,tralamazza/micropython,pfalcon/micropython,ryannathans/micropython,kerneltask/micropython,pfalcon/micropython,pozetroninc/micropython,henriknelson/micropython,swegener/micropython,tralamazza/micropython,adafruit/circuitpython,dmazzella/micropython,selste/micropython,pramasoul/micropython,tobbad/micropython,swegener/micropython,selste/micropython,ryannathans/micropython,selste/micropython,MrSurly/micropython,ryannathans/micropython,trezor/micropython,pozetroninc/micropython,tobbad/micropython,MrSurly/micropython,dmazzella/micropython,henriknelson/micropython,trezor/micropython,dmazzella/micropython,pfalcon/micropython,ryannathans/micropython,selste/micropython,adafruit/circuitpython,bvernoux/micropython,pozetroninc/micropython,bvernoux/micropython,adafruit/circuitpython,swegener/micropython,pramasoul/micropython,adafruit/micropython,MrSurly/micropython,pozetroninc/micropython,tobbad/micropython,swegener/micropython,henriknelson/micropython,adafruit/micropython,adafruit/circuitpython,kerneltask/micropython,bvernoux/micropython,pramasoul/micropython,henriknelson/micropython,kerneltask/micropython,tralamazza/micropython,MrSurly/micropython,pramasoul/micropython,tobbad/micropython,trezor/micropython,swegener/micropython,pfalcon/micropython,adafruit/circuitpython,tobbad/micropython,trezor/micropython,adafruit/micropython,MrSurly/micropython,tralamazza/micropython,pfalcon/micropython,pramasoul/micropython,dmazzella/micropython