powerpc/64s: Use generic permission masks

book3s64 need specific masks because it needs _PAGE_PRIVILEGED
for PAGE_NONE.

book3s64 already has _PAGE_RW and _PAGE_RWX.
So add _PAGE_NA, _PAGE_RO and _PAGE_ROX and remove specific
permission masks.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/d37a418de52e2c950cad6797e81663b56991366f.1695659959.git.christophe.leroy@csgroup.eu