Generalize the SpinLock and move it to AK.

Add a separate lock to protect the VFS. I think this might be a good idea.
I'm not sure it's a good approach though. I'll fiddle with it as I go along.

It's really fun to figure out all these things on my own.

VirtualFileSystem/VirtualFileSystem.h

@@ -5,6 +5,7 @@
 #include <AK/RetainPtr.h>
 #include <AK/String.h>
 #include <AK/Vector.h>
+#include <AK/Lock.h>
 #include "InodeIdentifier.h"
 #include "Limits.h"
 
@@ -15,6 +16,7 @@ class FileSystem;
 class VirtualFileSystem {
 public:
     static void initializeGlobals();
+    static SpinLock& lock();
 
     struct Node {
         InodeIdentifier inode;