Add initial IO APIC support

- IO APIC vector mapping
- Legacy PIC disable
- Real interrupts happening

src/kernel/interrupts.h

@@ -14,9 +14,11 @@ enum class isr : uint8_t
 #undef EISR
 #undef ISR
 
-	max
+	_zero = 0
 };
 
+isr operator+(const isr &lhs, int rhs);
+
 extern "C" {
 	void interrupts_enable();
 	void interrupts_disable();