stm32: Add STM32H7 family

Start adding support for the STM32H7 family of device and the first
available one the STM32H743.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>

BRANCH=none
BUG=b:67081508
TEST=manual, run on stm32h743i-eval and zerblebarn boards
get a stable serial console.

Change-Id: I9ae10f0d843e5318451713c21ed22d455a23758c
Reviewed-on: https://chromium-review.googlesource.com/806168
Commit-Ready: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>
Reviewed-by: Shawn N <shawnn@chromium.org>
11 files changed