cpu: Move current_tb field to CPUState

Explictly NULL it on CPU reset since it was located before breakpoints.

Change vapic_report_tpr_access() argument to CPUState. This also
resolves the use of void* for cpu.h independence.
Change vAPIC patch_instruction() argument to X86CPU.

Signed-off-by: Andreas Färber <afaerber@suse.de>
diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h
index f685c28..e856191 100644
--- a/include/exec/exec-all.h
+++ b/include/exec/exec-all.h
@@ -404,11 +404,13 @@
    instruction of a TB so that interrupts take effect immediately.  */
 static inline int can_do_io(CPUArchState *env)
 {
+    CPUState *cpu = ENV_GET_CPU(env);
+
     if (!use_icount) {
         return 1;
     }
     /* If not executing code then assume we are ok.  */
-    if (!env->current_tb) {
+    if (cpu->current_tb == NULL) {
         return 1;
     }
     return env->can_do_io != 0;