powerpc: remove outdated default on PCI_PERMEDIA

The Kconfig symbol PCI_PERMEDIA got removed in v2.6.24, through commit
e6b6e3ff ("[POWERPC] Remove APUS support
from arch/ppc"). Remove its last occurrence.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>