PPC: 440: Use 440 style MMU as default, so Qemu knows the MMU type

We have some KVM interaction code in Qemu that tries to be clever and
ignore some capabilities when running on BookE style MMUs. Unfortunately,
the default CPU bamboo was defaulting to was not a BookE-style MMU,
resulting in the check to fail.

With this patch, guests can run again on 440 with -enable-kvm.

Signed-off-by: Alexander Graf <agraf@suse.de>
