mm/gup: remove dead pgmap refcounting code

mm/gup: remove dead pgmap refcounting code

Prior to commit aed877c2b425 ("device/dax: properly refcount device dax
pages when mapping") ZONE_DEVICE pages were not fully reference counted
when mapped into user page tables.  Instead GUP would take a reference on
the associated pgmap to ensure the results of pfn_to_page() remained
valid.

This is no longer required and most of the code was removed by commit
fd2825b0760a ("mm/gup: remove pXX_devmap usage from get_user_pages()").
Finish cleaning this up by removing the dead calls to put_dev_pagemap()
and the temporary context struct.

Link: https://lkml.kernel.org/r/20250903225926.34702-1-apopple@nvidia.com
Signed-off-by: Alistair Popple <apopple@nvidia.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>