Use the I/O APIC when applicable.

src/acpi/madt.rs

src/acpi/mod.rs

src/acpi/rsdp.rs

src/arch/x86_64/device/ioapic.rs

src/arch/x86_64/device/mod.rs

src/arch/x86_64/device/pic.rs

src/arch/x86_64/interrupt/irq.rs

src/arch/x86_64/start.rs