powerpc: Remove arch/ppc cruft from Kconfig

Remove some leftover cruft from the arch/ppc days

Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Acked-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>