powerpc: Fix 64K page size support for PPC44x

powerpc: Fix 64K page size support for PPC44x

PPC44x supports page sizes other than 4K however when 64K page sizes
are selected compilation fails. This is due to a change in the
definition of pgtable_t introduced by the following patch:

commit 5c1f6ee9a31cbdac90bbb8ae1ba4475031ac74b4
Author: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
powerpc: Reduce PTE table memory wastage

The above patch only implements the new layout for PPC64 so it doesn't
compile for PPC32 with a 64K page size. Ideally we should implement
the same layout for PPC32 however for the meantime this patch reverts
the definition of pgtable_t for PPC32.

Signed-off-by: Alistair Popple <alistair@popple.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>