mmu-hash*: Remove permission checking from find_pte{32, 64}()

find_pte{32,64}() are poorly named, since they both find a PTE and do
permissions checking of it.  This patch makes them only locate a matching
PTE, moving the permission checking and other logic to the caller.  We
rename the resulting search functions ppc_hash{32,64}_htab_lookup().

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>
