KVM: PPC: Make real mode handler generic

The real mode handler code was originally writen for 64 bit Book3S only.
But since we not add 32 bit functionality too, we need to make some tweaks
to it.

This patch basically combines using the "long" access defines and using
fields from the shadow VCPU we just moved there.

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