Kernel: Scheduler now has reschedule()

This can be called from anywhere and just causes the scheduler to
schedule the next thread. This is more efficient and verbose version
of Scheduler::set_current_thread_sleeping(0), since we don't have
to wake other threads or do other verifications.

kernel/include/kernel/Scheduler.h

@@ -14,7 +14,9 @@ namespace Kernel
 		static Scheduler& get();
 
 		[[noreturn]] void start();
+
 		void timer_reschedule();
+		void reschedule();
 		void reschedule_if_idling();
 
 		void set_current_thread_sleeping(uint64_t);