IRQ 7 and 15 on the PIC architecture are used for spurious interrupts.
IRQ 7 could also be used for LPT connection, and IRQ 15 can be used for
the secondary IDE channel. Therefore, we need to allow to install a
real IRQ handler and check if a real IRQ was asserted. If so, we handle
them in the usual way.
A note on this fix - unregistering or registering a new IRQ handler
after we already registered one in the spurious interrupt handler is
not supported yet.
We don't return blindly the IRQ controller's model(), if the Spurious
IRQ handler is installed in IOAPIC environment, it's misleading to
return "IOAPIC" string since IOAPIC doesn't really handle Spurious
IRQs, therefore we return a "" string.
The IRQController object is RefCounted, and is shared between the
InterruptManagement class & IRQ handlers' classes.
IRQHandler, SharedIRQHandler & SpuriousInterruptHandler classes
use a responsible IRQ controller directly instead of calling
InterruptManagement for disable(), enable() or eoi().
Also, the initialization process of InterruptManagement is
simplified, so it doesn't rely on an ACPI parser to be initialized.
