accel/tcg: Move can_do_io to CPUNegativeOffsetState

Minimize the displacement to can_do_io, since it may
be touched at the start of each TranslationBlock.
It fits into other padding within the substructure.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
diff --git a/accel/dummy-cpus.c b/accel/dummy-cpus.c
index d6a1b8d..b75c919 100644
--- a/accel/dummy-cpus.c
+++ b/accel/dummy-cpus.c
@@ -27,7 +27,7 @@
     qemu_mutex_lock_iothread();
     qemu_thread_get_self(cpu->thread);
     cpu->thread_id = qemu_get_thread_id();
-    cpu->can_do_io = 1;
+    cpu->neg.can_do_io = true;
     current_cpu = cpu;
 
 #ifndef _WIN32