x86_64: charge clock cycles to threads when handling IRQs

Clock cycles that are used to handle the IRQ itself are *not*
charged to the thread.

arch/x86_64/irq.c

@@ -2,6 +2,7 @@
 #include <arch/ports.h>
 #include <arch/acpi.h>
 #include <socks/printk.h>
+#include <socks/sched.h>
 #include <socks/libc/string.h>
 #include <socks/machine/irq.h>
 #include <socks/machine/cpu.h>
@@ -232,11 +233,15 @@ void isr_dispatch(struct cpu_context *regs)
 
 void irq_dispatch(struct cpu_context *regs)
 {
+	end_charge_period();
+
 	irq_ack(regs->int_no);
 	struct queue *hooks = &irq_hooks[regs->int_no - IRQ0];
 	queue_foreach(struct irq_hook, hook, hooks, irq_entry) {
 		hook->irq_callback();
 	}
+
+	start_charge_period();
 }
 
 void syscall_dispatch(struct cpu_context *regs)