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
6 files changed