KVM: PPC: Remove 440 support

The 440 target hasn't been properly functioning for a few releases and
before I was the only one who fixes a very serious bug that indicates to
me that nobody used it before either.

Furthermore KVM on 440 is slow to the extent of unusable.

We don't have to carry along completely unused code. Remove 440 and give
us one less thing to worry about.

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