Improve psmfplayer seeking, audio pts sync

So the most risky change here is that this grabs audio pts values from the stream, rather than assuming they increase by 4180 linearly.  Most likely they do anyway, but this could either fix things or hurt things that were relying on our ignoring the actual audio pts values.

That fixes audio sync issues when seeking, though, wihch are hard to resolve when we the audio pts is made up.

This also uses the epmap to seek, which allows it to be fast.  I should do more testing, but it seems like the seek is basically ignored if there's no epmap.

Should fix #5438, does for the demo video anyway.  Only game I know of that uses initPts > 0.

-[Unknown]