vaapi: set libva message callbacks

This is available since the first commit after libva 0.39.4. Since the
version wasn't bumped since, we just check some random other symbol that
was added since (I'd rather not add a configure check).

The libva message callback repeats the endlessly repeated API mistakes
of libraries using global message callback handlers. But it's the only
way to shut up libva's dumb messages to stderr, so add something
complicated and dumb to workaround libva's stupidity.