pvr: fix deadlock caused by pollling channel group name

see title
This is not only a pvr issue. The gui calls into various modules while holding the gfx lock. The methods called should avoid grabbing other locks.

In the long run we should move away from this gui polling model, this also makes video stutter. Components should push/update their infos to some central place the gui and other components can access.

@opdenkamp mind a review?
@fritsch could you test this please