target/s390x: Use unwind data for helper_lra

Fix saving exception_index around mmu_translate; eliminate a dead store.
Reviewed-by: NAurelien Jarno <aurelien@aurel32.net>
Signed-off-by: NRichard Henderson <rth@twiddle.net>

target/s390x/mem_helper.c

@@ -1208,17 +1208,17 @@ uint64_t HELPER(lra)(CPUS390XState *env, uint64_t addr)
 {
     CPUState *cs = CPU(s390_env_get_cpu(env));
     uint32_t cc = 0;
-    int old_exc = cs->exception_index;
     uint64_t asc = env->psw.mask & PSW_MASK_ASC;
     uint64_t ret;
-    int flags;
+    int old_exc, flags;
 
     /* XXX incomplete - has more corner cases */
     if (!(env->psw.mask & PSW_MASK_64) && (addr >> 32)) {
+        cpu_restore_state(cs, GETPC());
         program_interrupt(env, PGM_SPECIAL_OP, 2);
     }
 
-    cs->exception_index = old_exc;
+    old_exc = cs->exception_index;
     if (mmu_translate(env, addr, 0, asc, &ret, &flags, true)) {
         cc = 3;
     }

target/s390x/translate.c

@@ -2565,7 +2565,6 @@ static ExitStatus op_lctlg(DisasContext *s, DisasOps *o)
 static ExitStatus op_lra(DisasContext *s, DisasOps *o)
 {
     check_privileged(s);
-    potential_page_fault(s);
     gen_helper_lra(o->out, cpu_env, o->in2);
     set_cc_static(s);
     return NO_EXIT;