Kernel: Add support for kernel addresses other than 3-4GB

Author: https://github.com/gunnarbeutner
Commit: b708b23b13
Pull-request: https://github.com/SerenityOS/serenity/pull/8795
Reviewed-by: https://github.com/Hendiadyoin1

Kernel/Arch/x86/PageDirectory.h

@@ -141,10 +141,11 @@ class PageDirectoryPointerTable {
 public:
     PageDirectoryEntry* directory(size_t index)
     {
+        VERIFY(index <= (NumericLimits<size_t>::max() << 30));
         return (PageDirectoryEntry*)(PhysicalAddress::physical_page_base(raw[index]));
     }
 
-    u64 raw[4];
+    u64 raw[512];
 };
 
 }