Kernel: Add SMP IPI support

We can now properly initialize all processors without
crashing by sending SMP IPI messages to synchronize memory
between processors.

We now initialize the APs once we have the scheduler running.
This is so that we can process IPI messages from the other
cores.

Also rework interrupt handling a bit so that it's more of a
1:1 mapping. We need to allocate non-sharable interrupts for
IPIs.

This also fixes the occasional hang/crash because all
CPUs now synchronize memory with each other.

Kernel/Process.cpp

@@ -1271,7 +1271,7 @@ int Process::exec(String path, Vector<String> arguments, Vector<String> environm
         // We need to enter the scheduler lock before changing the state
         // and it will be released after the context switch into that
         // thread. We should also still be in our critical section
-        ASSERT(!g_scheduler_lock.is_locked());
+        ASSERT(!g_scheduler_lock.own_lock());
         ASSERT(Processor::current().in_critical() == 1);
         g_scheduler_lock.lock();
         current_thread->set_state(Thread::State::Running);