Reclaim bootloader page table pages

src/hulk/pagetable.d

@@ -136,8 +136,11 @@ static assert(PageTableEntry.sizeof == 8u);
  */
 struct PageTable
 {
+    /** Number of page table entries in a page table. */
+    enum size_t N_ENTRIES = 512u;
+
     /** Page table entries. */
-    private PageTableEntry[512] entries;
+    private PageTableEntry[N_ENTRIES] entries;
 
     /**
      * Access the PageTableEntry for the given address and page table level.