Add dynamic interrupt allocation mechanism
This adds:
- Dynamic allocation of interrupts. Pass it the features of the interrupt you want, it'll set you up with an int.
- Shared interrupts. Enables multiple peripheral drivers to use the same interrupt.
- Marking what interrupts are fully executable from IRAM; if an int isn't marked like that it will get disabled once flash cache gets disabled.
Also:
- Modifies driver to be in line with these changes
See merge request !254
