powerpc: Remove suspect CONFIG_PPC_BOOK3E #ifdefs in nohash/64/pgtable.h

There are three #ifdef CONFIG_PPC_BOOK3E sections in nohash/64/pgtable.h.
And there should be no configurations possible which use nohash/64/pgtable.h
but don't also enable CONFIG_PPC_BOOK3E.

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