kernel: fix some TODOs

kernel/arch/x86_64/src/mem/table.rs

@@ -213,6 +213,11 @@ impl<L: EntryLevel> PageTable<L> {
         Ok(table)
     }
 
+    pub unsafe fn free<TA: TableAllocator>(this: PhysicalRefMut<Self, KernelTableManagerImpl>) {
+        let physical = this.as_physical_address();
+        TA::free_page_table(physical);
+    }
+
     // /// Returns the physical address of this table
     // pub fn physical_address(&self) -> usize {
     //     unsafe { (self.data.as_ptr() as usize).physicalize() }