arm64: mm: call pagetable dtor when freeing hot-removed page tables

In the Linux kernel, the following vulnerability has been resolved:

arm64: mm: call pagetable dtor when freeing hot-removed page tables

Since 5e8eb9aeeda3 ("arm64: mm: always call PTE/PMD ctor in
__create_pgd_mapping()") page-table allocation on ARM64 always calls
pagetable_{pte,pmd,pud,p4d}_ctor(). This sets the page_type to
PGTY_table, increments NR_PAGETABLE and possible allocates a PTL. However
the matching pagetable_dtor() calls were never added.

With DEBUG_VM enabled on kernel versions prior to v6.17 without
2dfcd1608f3a9 ("mm/page_alloc: let page freeing clear any set page type")
this leads to the following warning when freeing these pages due to
page->page_type sharing page->_mapcount:

BUG: Bad page state in process ... pfn:284fbb
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x284fbb
flags: 0x17fffc000000000(node=0|zone=2|lastcpupid=0x1ffff)
page_type: f2(table)
page dumped because: nonzero mapcount
Call trace:
bad_page+0x13c/0x160
__free_frozen_pages+0x6cc/0x860
___free_pages+0xf4/0x180
free_pages+0x54/0x80
free_hotplug_page_range.part.0+0x58/0x90
free_empty_tables+0x438/0x500
__remove_pgd_mapping.constprop.0+0x60/0xa8
arch_remove_memory+0x48/0x80
try_remove_memory+0x158/0x1d8
offline_and_remove_memory+0x138/0x180

It can also lead to leaking the ptl allocation if ALLOC_SPLIT_PTLOCKS is
defined and incorrect NR_PAGETABLE stats. Fix this by calling
pagetable_dtor() in free_hotplug_pgtable_page() prior to freeing the page
to undo the effects of calling pagetable_*_ctor().