Avoid key_queue_mutex deadlock in waitkey()

Waitkey() is designed to obtain lock "key_queue_mutex" in
the very beginning of function.

  int RecoveryUI::WaitKey() {
    std::unique_lock<std::mutex> lk(key_queue_mutex);
    ...
  }

However, there's case "key_queue_mutex" being applied again in
waitkey(), thus cause deadlock. There are two reproduce
scenario:
1.Executing "fastboot reboot recovery" in userspace
  fastboot
2.Executing "adb reboot fastboot" in recovery os

When entering userspace fastboot/recovery, waitkey()
will wait there for user action. fastboot/adb commands
will trigger ui->interruptkey() to notify the thread
waitkey() in. In the next, waitkey() will move on and call
SetScreenSaveState(), which do LOG(ERROR) in fail case of
brightness set. LOG(ERROR) is designed to print log on
UI. Unfortunately, UI->print() applies lock "key_queue_mutex"
too, so deadlock happen.

Note:
Here is details how lock "key_queue_mutex" applied in
UI->print():
Function Print() call
   Function PrintV() call
      Function update_screen_locked() call
         Function draw_screen_locked() call
            Function draw_menu_and_test_buffer_locked() call
               Function IsLongPress()

  bool RecoveryUI::IsLongPress() {
    std::lock_guard<std::mutex> lg(key_queue_mutex);
    bool result = key_long_press;
    return result;
  }

Bug: 135078366
Test: no errors when running "fastboot reboot recovery" in userspace
      fastboot & "adb reboot fastboot" in recovery os

Change-Id: Ida6b3c4ba9896a70021373f02a94954f0a60cf31
Signed-off-by: Zhang, GaofengX <gaofengx.zhang@intel.com>
Signed-off-by: Xihua Chen <xihua.chen@intel.com>