KVM: PPC: Make software load/store return eaddr

The Book3S KVM implementation contains some helper functions to load and store
data from and to virtual addresses.

Unfortunately, this helper used to keep the physical address it so nicely
found out for us to itself. So let's change that and make it return the
physical address it resolved.

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