powerpc/nohash: Deduplicate pte helpers

Deduplicate following helpers that are identical on
nohash/32 and nohash/64:
  pte_mkwrite_novma()
  pte_mkdirty()
  pte_mkyoung()
  pte_wrprotect()
  pte_mkexec()
  pte_young()

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/485f3cbafaa948143f92692e17ca652dfed68da2.1695659959.git.christophe.leroy@csgroup.eu