powerpc/mm: Move hash64 PTE bits from book3s/64/pgtable.h to hash.h

This enables us to keep hash64 related bits together, and makes it easy
to follow.

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