Implement interfaces for MHL scratchpad command

1. Add sendScratchpadCommand to IHdmiControlService interface,
which is used to send scratchpad command.

2. Add IHdmiMhlScratchpadCommandListener to handle incoming
MHL scratchpad command.

Bug: 17146522

Change-Id: I8e8e743dc08a18c80867be470997ce79d3292c15
diff --git a/Android.mk b/Android.mk
index 80b860b..6280332 100644
--- a/Android.mk
+++ b/Android.mk
@@ -156,6 +156,7 @@
 	core/java/android/hardware/hdmi/IHdmiDeviceEventListener.aidl \
 	core/java/android/hardware/hdmi/IHdmiHotplugEventListener.aidl \
 	core/java/android/hardware/hdmi/IHdmiInputChangeListener.aidl \
+	core/java/android/hardware/hdmi/IHdmiMhlScratchpadCommandListener.aidl \
 	core/java/android/hardware/hdmi/IHdmiRecordListener.aidl \
 	core/java/android/hardware/hdmi/IHdmiSystemAudioModeChangeListener.aidl \
 	core/java/android/hardware/hdmi/IHdmiVendorCommandListener.aidl \