[POWERPC] disallow building powermac and tsi108 without PCI

The TSI108 code and the 32 bit powermac and chrp platforms
have dependency on PCI that is not easy or desirable to get rid
of.

The easiest fix is to always select CONFIG_PCI if one of those
platforms is enabled.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>