ppc: Change 'invalid' bit mask of tlbiel and tlbie

Otherwise it will trip on the forms used in recent architecture.

Ideally, we should have different handlers for different architecture
levels but our current implementation of TLB flushing is dumb enough
that this will do for now.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
