HdmiCecControl: Log messages from libcec
HdmiCecControl: Log messages from libcec

With debug enabled, this logs 220 messages at startup, but only 2
messages per keypress.

I figured out the API by looking at the example Python client in the
libcec source repo:
https://github.com/Pulse-Eight/libcec/blob/libcec-3.0.1/src/pyCecClient/pyCecClient.py

stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester