Support "Mute" and "Restore Volume" CEC commands

Adds support for <User Control Pressed> ["Mute Function"] and ["Restore
Volume Function"] on all HDMI devices. These commands are currently
ignored because they are not mapped to an Android keycode.

Support for these commands is required for HDMI CEC 2.0.

Bug: 191230341
Test: Manual; atest HdmiCecLocalDeviceTest
Change-Id: I5146e9e99595a9a124e0ce2176f5e70a29923a49