interrupt: Add convenience macros for enable/disable

[oliv3r]

While any seasoned AVR developer should have memorized cli/sei by heart, not everybody is as seasoned or mindful. Further, the three letter accronym also isn't directly discriptive.

Lets introduce a simple macro, similar to 'power_all_disable' etc, to enable/disable interrupts in a more readable way.

[3-14152898]

(I'm aware I'm late to the show, sorry for that.)

Wouldn't it make even more sense to name those macros interrupt_all_disable/interrupt_all_enable instead, in the same vein as the example you've used as an illustration? Both sei and cli affect interrupts globally, just like power_all_disable affects power savings globally.