parisc: Define and use set_pte_at()

When a PTE is changed, we need to flush the PTE. set_pte_at()
was lost in the folio update. PA-RISC version is the same as
the generic version.

Signed-off-by: John David Anglin <dave.anglin@bell.net>
Signed-off-by: Helge Deller <deller@gmx.de>
Cc: stable@vger.kernel.org # v5.12+