target-ppc: Fix htab_mask calculation

Correctly update the htab_mask using the return value of
KVM_PPC_ALLOCATE_HTAB ioctl. Also we don't update sdr1
on GET_SREGS for HV. We check for external htab and if
found true, we don't need to update sdr1

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
[ fixed pte group offset computation in ppc_hash64_htab_lookup() that
  caused TCG to fail, Greg Kurz <gkurz@linux.vnet.ibm.com> ]
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/target-ppc/misc_helper.c b/target-ppc/misc_helper.c
index 616aab6..dc2ebfc 100644
--- a/target-ppc/misc_helper.c
+++ b/target-ppc/misc_helper.c
@@ -38,7 +38,9 @@
 
 void helper_store_sdr1(CPUPPCState *env, target_ulong val)
 {
-    ppc_store_sdr1(env, val);
+    if (!env->external_htab) {
+        ppc_store_sdr1(env, val);
+    }
 }
 
 void helper_store_hid0_601(CPUPPCState *env, target_ulong val)