powerpc: disable CHRP and PMAC support in various defconfigs

Because CHRP and PMAC are by default enabled, several non-CHRP and non-PMAC
PowerPC defconfigs will have these Kconfig options set erroneously.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>