Clean up the currently available memory models for ppc32 under
the powerpc architecture.  We need FLATMEM for ppc32: enable it.
SPARSEMEM is not parameterised for ppc32 so disable that.  Take this
opportunity to clean up white space for FLATMEM_ENABLE.
Signed-off-by: NAndy Whitcroft <apw@shadowen.org>
Signed-off-by: NPaul Mackerras <paulus@samba.org>