Kernel: Fix counting interrupts

Move counting interrupts out of the handle_interrupt method so that
it is done in all cases without the interrupt handler having to
implement it explicitly.

Also make the counter an atomic value as e.g. the LocalAPIC interrupts
may be triggered on multiple processors simultaneously.

Fixes #4297

Kernel/Interrupts/SharedIRQHandler.cpp

@@ -87,7 +87,6 @@ SharedIRQHandler::~SharedIRQHandler()
 void SharedIRQHandler::handle_interrupt(const RegisterState& regs)
 {
     ASSERT_INTERRUPTS_DISABLED();
-    increment_invoking_counter();
 #ifdef INTERRUPT_DEBUG
     dbg() << "Interrupt @ " << interrupt_number();
     dbg() << "Interrupt Handlers registered - " << m_handlers.size();