iov: remove copy_page_from_iter_atomic()

All callers now use copy_folio_from_iter_atomic(), so convert
copy_page_from_iter_atomic().  While I'm in there, use kmap_local_folio()
and pagefault_disable() instead of kmap_atomic().  That allows preemption
and/or task migration to happen during the copy_from_user().  Also use the
new folio_test_partial_kmap() predicate instead of open-coding it.

Link: https://lkml.kernel.org/r/20250514170607.3000994-4-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Hugh Dickins <hughd@google.com>
Cc: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>