[PATCH] powerpc32: clean up available memory models

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: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>