cpu: Move singlestep_enabled field from CPU_COMMON to CPUState

Prepares for changing cpu_single_step() argument to CPUState.

Acked-by: Michael Walle <michael@walle.cc> (for lm32)
Signed-off-by: Andreas Färber <afaerber@suse.de>
diff --git a/exec.c b/exec.c
index c8658c6..30b676d 100644
--- a/exec.c
+++ b/exec.c
@@ -588,11 +588,13 @@
 void cpu_single_step(CPUArchState *env, int enabled)
 {
 #if defined(TARGET_HAS_ICE)
-    if (env->singlestep_enabled != enabled) {
-        env->singlestep_enabled = enabled;
-        if (kvm_enabled())
+    CPUState *cpu = ENV_GET_CPU(env);
+
+    if (cpu->singlestep_enabled != enabled) {
+        cpu->singlestep_enabled = enabled;
+        if (kvm_enabled()) {
             kvm_update_guest_debug(env, 0);
-        else {
+        } else {
             /* must flush all the translated code to avoid inconsistencies */
             /* XXX: only flush what is necessary */
             tb_flush(env);