Just as I wanted to write that everything works ok with uvd enabled and this
bug can be closed, after the 19th suspend/hibernate attempt the machine failed
to resume, with the screen simply going black and reporting no signal :-(

I've tried to resume from the same image 5 times but to no avail, so I'm back
now with radeon.no_uvd=1 for a while to give it a test with real-world usage
pattern. Just to be sure that this works in all cases too.