Kernel: Move SpinLock.h into Locking/

Author: https://github.com/boricj
Commit: 2c3b0baf76
Pull-request: https://github.com/SerenityOS/serenity/pull/8851
Reviewed-by: https://github.com/awesomekling ✅
Reviewed-by: https://github.com/bgianfo

Kernel/Locking/Mutex.cpp

@@ -10,7 +10,7 @@
 #include <Kernel/Debug.h>
 #include <Kernel/KSyms.h>
 #include <Kernel/Locking/Mutex.h>
-#include <Kernel/SpinLock.h>
+#include <Kernel/Locking/SpinLock.h>
 #include <Kernel/Thread.h>
 
 namespace Kernel {