MdeModulePkg: Avoid key notification called more than once

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=996

Issue:
In current code logic, when a key is pressed, it will search
the whole NotifyList to find whether a notification has been
registered with the keystroke. if yes, it will en-queue the
key for notification execution later. And now if different
notification functions have been registered with the same key,
then the key will be en-queued more than once. Then it will
cause the notification executed more than once.

This patch is to enhance the code logic to fix this issue.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>

MdeModulePkg/Bus/Isa/Ps2KeyboardDxe/Ps2KbdCtrller.c

@@ -1451,6 +1451,7 @@ KeyGetchar (
       //
       PushEfikeyBufTail (&ConsoleIn->EfiKeyQueueForNotify, &KeyData);
       gBS->SignalEvent (ConsoleIn->KeyNotifyProcessEvent);
+      break;
     }
   }
 

MdeModulePkg/Bus/Usb/UsbKbDxe/KeyBoard.c

@@ -1695,6 +1695,7 @@ UsbKeyCodeToEfiInputKey (
       //
       Enqueue (&UsbKeyboardDevice->EfiKeyQueueForNotify, KeyData, sizeof (*KeyData));
       gBS->SignalEvent (UsbKeyboardDevice->KeyNotifyProcessEvent);
+      break;
     }
   }
 

MdeModulePkg/Universal/Console/TerminalDxe/TerminalConIn.c

@@ -987,6 +987,7 @@ EfiKeyFiFoInsertOneKey (
       //
       EfiKeyFiFoForNotifyInsertOneKey (TerminalDevice->EfiKeyFiFoForNotify, Key);
       gBS->SignalEvent (TerminalDevice->KeyNotifyProcessEvent);
+      break;
     }
   }
   if (IsEfiKeyFiFoFull (TerminalDevice)) {