Kernel: Let Processor::is_initialized() of aarch64 return false

When calling dbgln(), the formatting code in AK/Format.h calls
Processor::is_initialized() to determine whether to add some text about
the current processor to the debug output. Instead of crashing, we just
return false, such that we can use dbgln() etc in the aarch64 Kernel.

Kernel/Arch/aarch64/Processor.h

@@ -66,7 +66,6 @@ public:
 
     ALWAYS_INLINE static bool is_initialized()
     {
-        VERIFY_NOT_REACHED();
         return false;
     }