[OMXPlayer, Feature, RFC] Both HDMI and Analog audio output

WARNING: first firmware, that support this code, is from Feb 7. Before it, this code lead to system hang!

Idea for this code come from request in other fan repo and is around 2 moths old:

> Hello,
> 
> I have a hearing problem and listen to the movies on a device that is connected to the analog input of the Raspberry Pi. My wife would also like to hear sound and her sound is given by the TV via HDMI.
> Now the problem is that the sound goes through HDMI or analog output.
> 
> It would be great if the audio through both HDMI and analog would be sent so we both can enjoy the movie. Is this possible?

During New Year holidays i found some free time and decide to do something for such people. Now, when we have working firmware, it is time to propose this code for upstream.

As you can expect, there is some (even minimal) delay between 2 outputs, but in context of request purpose, i believe it is acceptable. Assumption was made that HDMI is active (actually i can't test it without connected and active HDMI).