USE COMMON VECTOR LOGIC IN ALL ARM ARCHITECTURES.

```
Description: Originally, each ARMv7-M MCU architecture had its own
private implementation for interrupt vectors and interrupt
handling logic. This was superseded by common interrupt
vector logic but these private implementations were never
removed from older MCU architectures. This is turning into
a maintenance issue because any improvements to the common
vector handling must also be re-implemented for each of the
older MCU architectures.
Status: Open
Priority: Low. A pain in the ass and an annoying implementation, but
not really an issue otherwise.
```