Adapt some Examples 2.x to ARM CM4 Core on STM32F446

[ckormanyos]

As discussed toward the end of #273, Adapt some Examples 2.x to ARM CM4 Core on STM32F446.

Cc: @jvco98

[ckormanyos]

I'm actually liking the stm32h7a3 target for this issue due to its simple startup and clock initialization and the fact that it gets this issue up to ARM(R) CM7 core.

[ckormanyos]

liking the stm32h7a3 target

Or Teensy 4.0 because of its more closely coupled shared heritage with Arduino through Teensy-Duino.