cso: don't release sampler states that are bound

cso: don't release sampler states that are bound

This fixes random radeonsi GPU hangs in Batman Arkham: Origins (Wine) and
probably many other games too.

cso_cache deletes sampler states when the cache size is too big and doesn't
check which sampler states are bound, causing use-after-free in drivers.
Because of that, radeonsi uploaded garbage sampler states and the hardware
went bananas. Other drivers may have experienced similar issues.

Cc: 12.0 13.0 <mesa-stable@lists.freedesktop.org>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Reviewed-by: Edward O'Callaghan <funfunctor@folklore1984.net>