PPC: openpic_kvm: Filter memory events properly

Commit 6f1834a2b exposed a bug in openpic_kvm where we don't filter
for memory events that only happen to the region we want to know
events about.

Add proper filtering, fixing the e500plat target with KVM.

Signed-off-by: Alexander Graf <agraf@suse.de>
Message-id: 1396431718-14908-1-git-send-email-agraf@suse.de
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
