KVM: PPC: Make Alignment interrupts work again

In the process of merging Book3S_32 and 64 I somehow ended up having the
alignment interrupt handler take last_inst, but the fetching code not
fetching it. So we ended up with stale last_inst values.

Let's just enable last_inst fetching for alignment interrupts too.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>