KVM: PPC: Make highmem code generic

Since we now have several fields in the shadow VCPU, we also change
the internal calling convention between the different entry/exit code
layers.

Let's reflect that in the IR=1 code and make sure we use "long" defines
for long field access.

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