Remapping these registers every time we try to read from or write to
them causes a lot of SMP broadcasts and a lot of other overhead.
This improves boot time noticeably.
Instead of blindly setting masks, if we want to disable an IRQ and it's
already masked, we just return. The same happens if we want to enable an
IRQ and it's unmasked.
Now we don't send raw numbers, but we let the IRQController object to
figure out the correct IRQ number.
This helps in a situation when we have 2 or more IOAPICs, so if IOAPIC
1 is assigned for IRQs 0-23 and IOAPIC 2 is assigned for IRQs 24-47,
if an IRQHandler of IRQ 25 invokes disable() for example, it will call
his responsible IRQController (IOAPIC 2), and the IRQController will
subtract the IRQ number with his assigned offset, and the result is that
the second redirection entry in IOAPIC 2 will be masked.
Also, InterruptDisabler were added to prevent critical function from
being interrupted. In addition, the interrupt numbers are abstracted
from IDT offsets, thus, allowing to create a better routing scheme
when using IOAPICs for interrupt redirection.
