Kernel: Make PageDirectory.cpp compile on aarch64

Author: https://github.com/jamesmintram
Commit: d3b6201b40
Pull-request: https://github.com/SerenityOS/serenity/pull/13447

Kernel/Memory/PageDirectory.cpp

@@ -6,6 +6,8 @@
 
 #include <AK/Memory.h>
 #include <AK/Singleton.h>
+#include <Kernel/Arch/CPU.h>
+#include <Kernel/Arch/PageDirectory.h>
 #include <Kernel/Memory/MemoryManager.h>
 #include <Kernel/Memory/PageDirectory.h>
 #include <Kernel/Prekernel/Prekernel.h>