Allow PiP when using a VAAPI playback profile

Two VAAPI streams at once still doesn't work (causes video corruption), but still should be able to use PiP regardless.

(cherry picked from commit 4a289572b54f076443f295cfae21f77e6d0f4d93)

Conflicts:
	mythtv/libs/libmythtv/vaapicontext.cpp