[cec] rebased PR1794 + fix for Frodo

@davilla these are the changes from #1794 rebased onto Frodo and squashed. this bumps libCEC to 2.1.0 too, so your choice whether you want to pull this, but I recommend doing so because it fixes a bunch of issues:
- CEC adapter not detected by XBMC on OSX when running firmware v3+
- CEC stopped working on the Pi with certain AVRs that provided an invalid physical address while in standby. libCEC now listens to HPD on the Pi and rereads the address when needed
- some vendor specific issues
- hacks to get things working in XBMC for the Pi removed, and support for other devices, such as the TDA995x, added