stm32: Document flash layout for 1 MB Flash (STM32F412)
stm32: Document flash layout for 1 MB Flash (STM32F412)

STM32F412xE has 512 KB flash
STM32F412xG has 1 MB flash

https://www.st.com/resource/en/datasheet/stm32f412cg.pdf

BRANCH=none
BUG=none
TEST=make buildall -j

Change-Id: I260659a1de62f3e79f427dd38ca831b4cabed448
Signed-off-by: Tom Hughes <fc5c12f30a5ed2baa0581f44ee14ad1eb7b20d83@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1902463
Reviewed-by: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec