powerpc/mm/keys: Move pte bits to correct headers

Memory keys are supported only with hash translation mode. Instead of
using #ifdef in generic code move the key related pte bits to
respective headers

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>