soc: adi: max32: Use fixed MPU regions

Default MPU configuration marks whole flash area as cacheable. When
reading from an erased section of flash, cache controller may fill cache
lines with ECC corrected data. To prevent this, disable caching on
storage section so that ECC workaround can be applied during reads and
correct data is returned.

Signed-off-by: Tahsin Mutlugun <Tahsin.Mutlugun@analog.com>