Add HDMI hotplug events to dumpsys hdmi_control

To help with debugging wake-up and HDMI CEC address allocation issues.
Hotplug events and CEC messages will be interleaved in dumpsys
hdmi_control.

This information will be captured in bugreports.

Test: adb shell dumpsys hdmi_control
BUG=149679124

Change-Id: Ic918155b00e242b40c88d72089479127ba095b37