stm32/sdram: Update MPU settings to block invalid region, change attrs.
stm32/sdram: Update MPU settings to block invalid region, change attrs.

Set the active MPU region to the actual size of SDRAM configured and
invalidate the rest of the memory-mapped region, to prevent errors due to
CPU speculation.  Also update the attributes of the SDRAM region as per ST
recommendations, and change region numbers to avoid conflicts elsewhere in
the codebase (see eth usage).

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