allow recovery UI to ignore certain keypresses

Change-Id: Id182bb95ffcc475c5acabb29b413e422302ae7f2

ui.cpp

@@ -123,6 +123,9 @@ void RecoveryUI::process_key(int key_code, int updown) {
 
     if (register_key) {
         switch (CheckKey(key_code)) {
+          case RecoveryUI::IGNORE:
+            break;
+
           case RecoveryUI::TOGGLE:
             ShowText(!IsTextVisible());
             break;

ui.h

@@ -73,7 +73,7 @@ class RecoveryUI {
     // Return value indicates whether an immediate operation should be
     // triggered (toggling the display, rebooting the device), or if
     // the key should be enqueued for use by the main thread.
-    enum KeyAction { ENQUEUE, TOGGLE, REBOOT };
+    enum KeyAction { ENQUEUE, TOGGLE, REBOOT, IGNORE };
     virtual KeyAction CheckKey(int key);
 
     // --- menu display ---