Update mesa to 20.1.5
Update amber-phone's mesa to 20.1 for much better stability and rendering correctness, based on Debian's packaging.
Since the reason for hangs in 20.1 (anisotropic filtering) has been found, I've reverted it and therefore obsoleted !2 (closed) with this MR. The rest of reasoning from !2 (closed) still applies.
Edited by Sebastian Krzyszkowiak