Let's do the same as we did for uv_destroy_(folio|pte)() and
have the following variants:

(1) uv_convert_from_secure(): "low level" helper that operates on paddr
and does not mess with folios.

(2) uv_convert_from_secure_folio(): Consumes a folio to which we hold a
reference.

(3) uv_convert_from_secure_pte(): Consumes a PTE that holds a reference
through the mapping.

Unfortunately we need uv_convert_from_secure_pte(), because pfn_folio()
and friends are not available in pgtable.h.
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20240508182955.358628-9-david@redhat.comSigned-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>