powerpc/mm: Delete booke bits from book3s

We also move __ASSEMBLY__ towards the end of header. This avoid
having #ifndef __ASSEMBLY___ all over the header

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>