Kernel/Interrupts: Return boolean on whether we handled the interrupt

If we are in a shared interrupt handler, the called handlers might
indicate it was not their interrupt, so we should not increment the
call counter of these handlers.

Kernel/Time/RTC.h

@@ -31,6 +31,6 @@ public:
 
 private:
     explicit RealTimeClock(Function<void(const RegisterState&)> callback);
-    virtual void handle_irq(const RegisterState&) override;
+    virtual bool handle_irq(const RegisterState&) override;
 };
 }