Kernel: Optimize scheduler idling

Now after each interrupt we will ask the scheduler to reschedule
if the current thread is the idle thread. This allows semaphore
unblocking to be practically instant when there is only one thread
executing.

Now disk reading is back to ~3 MB/s for single threaded process

kernel/arch/x86_64/IDT.cpp

@@ -3,6 +3,7 @@
 #include <kernel/InterruptController.h>
 #include <kernel/kmalloc.h>
 #include <kernel/Panic.h>
+#include <kernel/Scheduler.h>
 
 #define REGISTER_ISR_HANDLER(i) register_interrupt_handler(i, isr ## i)
 #define REGISTER_IRQ_HANDLER(i) register_interrupt_handler(IRQ_VECTOR_BASE + i, irq ## i)
@@ -129,6 +130,8 @@ namespace IDT
 		// NOTE: Scheduler sends PIT eoi's
 		if (irq != PIT_IRQ)
 			InterruptController::get().eoi(irq);
+
+		Kernel::Scheduler::get().reschedule_if_idling();
 	}
 
 	static void flush_idt()