arm/arm-powerctl: rebuild hflags after setting CP15 bits in arm_set_cpu_on()

After setting CP15 bits in arm_set_cpu_on() the cached hflags must
be rebuild to reflect the changed processor state. Without rebuilding,
the cached hflags would be inconsistent until the next call to
arm_rebuild_hflags(). When QEMU is compiled with debugging enabled
(--enable-debug), this problem is captured shortly after the first
call to arm_set_cpu_on() for CPUs running in ARM 32-bit non-secure mode:

  qemu-system-arm: target/arm/helper.c:11359: cpu_get_tb_cpu_state:
  Assertion `flags == rebuild_hflags_internal(env)' failed.
  Aborted (core dumped)

Fixes: 0c7f8c43da
Cc: qemu-stable@nongnu.org
Signed-off-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/arm-powerctl.c

@@ -127,6 +127,9 @@ static void arm_set_cpu_on_async_work(CPUState *target_cpu_state,
         target_cpu->env.regs[0] = info->context_id;
     }
 
+    /* CP15 update requires rebuilding hflags */
+    arm_rebuild_hflags(&target_cpu->env);
+
     /* Start the new CPU at the requested address */
     cpu_set_pc(target_cpu_state, info->entry);