KVM: PPC: Book3S PR: Invalidate SLB entries properly

At present, if the guest creates a valid SLB (segment lookaside buffer)
entry with the slbmte instruction, then invalidates it with the slbie
instruction, then reads the entry with the slbmfee/slbmfev instructions,
the result of the slbmfee will have the valid bit set, even though the
entry is not actually considered valid by the host.  This is confusing,
if not worse.  This fixes it by zeroing out the orige and origv fields
of the SLB entry structure when the entry is invalidated.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>