stm32f4: mpu: Add support for 1.5MB Flash / 320kB SRAM variants

The STM32F413ZH has 1536kB of Flash and 320kB of SRAM. This
configuration is currently not supported by ST MPU driver, so fill in
the blanks.

Note: The MPU does not support region size that is not a power-of-2 (see
the SIZE field in the MPU_RASR register). This is a problem for our
1536kB Flash region, so it was rounded up to the nearest choice. This is
possible because the memory in the range 0x0818000 - 0x0FFFFFFF is
"Reserved" and thus not mapped anyway.

Change-Id: If0c3d1db564ca45e77f8b5bafa2afdbafa85b40f
Signed-off-by: Florian Vaussard <florian.vaussard@heig-vd.ch>