[POWERPC] Further fixes for the removal of 4level-fixup hack from ppc32

Commit d1953c88 removed the use of
4level-fixup.h for 32-bit systems under arch/powerpc.  However, I
missed a few things activated on some configurations, resulting in
some warnings (at least with STRICT_MM_TYPECHECKS enabled) and build
errors in some circumstances.  This fixes it.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>