Fix clocking configuration issues on STM32H7x processors

Hi, could someone provide some background / insight into why the clocking / voltage issues identified and fixed by:

https://github.com/mbed-ce/mbed-os/pull/262

and then adopted by

https://github.com/ARMmbed/mbed-os/pull/15502

have not been applied to the Arduino fork of mbed-os?

Update: Having looked through these PRs, the undervolting issue appears unaddressed and is concerning me.

Start by comparing the clocking and voltage changes in mbed-ce/mbed-os PR 262 and ARMmbed/mbed-os PR 15502 with the STM32H7x support in this ArduinoCore-mbed fork. Trace the relevant processor configuration entry points and determine whether the undervolting fix is absent. Done means documenting the difference and identifying the specific configuration change needed.

Written by the indexing model from the issue text.