mm/debug_vm_pgtable: use a swp_entry_t input value for swap tests

mm/debug_vm_pgtable: use a swp_entry_t input value for swap tests

The various __pte/pmd_to_swp_entry and __swp_entry_to_pte/pmd helper
functions are expected to operate on swap PTE/PMD entries, not on present
and mapped entries.

Reflect this in the swap tests by using a swp_entry_t as input value, and
convert it to a swap PTE/PMD for testing, similar to how it is already
done in pte_swap_exclusive_tests().  Move the swap entry creation from
there to init_args() and store it in args, so it can also be used in other
functions.

The pte/pmd_swap_tests() are also changed to compare entries instead of
pfn values, again similar to pte_swap_exclusive_tests().  pte/pmd_pfn()
helpers are also not expected to operate on swap PTE/PMD entries at all.

Also update documentation, to reflect that the helpers operate on swap
PTE/PMD entries and not present and mapped entries, and use correct names,
i.e.  __swp_to_pte/pmd_entry -> __swp_entry_to_pte/pmd.

For consistency, also change pte/pmd_swap_soft_dirty_tests() to use
args->swp_entry instead of a present and mapped PTE/PMD.

Link: https://lore.kernel.org/all/20250623184321.927418-1-gerald.schaefer@linux.ibm.com
Link: https://lkml.kernel.org/r/20250630164726.930405-1-gerald.schaefer@linux.ibm.com
Signed-off-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>