winsys/amdgpu: enlarge buffer_indices_hashlist

winsys/amdgpu: enlarge buffer_indices_hashlist

Enlarge the buffer hashlist to prevent large numbers of misses
due to adding more buffers than can be cached in the hashlist.

The game I tested had CS's with up to 1500 buffers and the overhead
of amdgpu_lookup_buffer for various sizes was:

4096 1.97% (new value)
2048 4.37%
1024 6.92%
512  9.47% (old value)

(percentage of CPU usage in render thread as determined by perf)

The time spent in amdgpu_add_buffer self is ~4.2% in all cases and
for 4096 the time needed to clear the hashlist is still < 0.10%,
so I am not expecting significant regressions.

Signed-off-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Signed-off-by: Marek Olšák <marek.olsak@amd.com>