Kernel: Split initialization of Processor structure

We need to very early on initialize the Processor structure so
that we can use RecursiveSpinLock early on.

Kernel/Arch/i386/CPU.h

@@ -639,6 +639,7 @@ class Processor {
     static Vector<Processor*>& processors();
 
 public:
+    void early_initialize(u32 cpu);
     void initialize(u32 cpu);
 
     Descriptor& get_gdt_entry(u16 selector);