powerpc/nohash: Refactor pte_clear()

pte_clear() are doing the same on nohash/32 and nohash/64,

Keep the static inline version of nohash/64, make it common and
remove the macro version of nohash/32.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/818f7df83d7e9e18f55e274cd3c44f2871ade4dd.1695659959.git.christophe.leroy@csgroup.eu