The RDNA3.5 config table selects a 64-row / 128-thread tile up to J=32 and a
128-row / 256-thread tile above that. On gfx115x the smaller tile leaves enough
LDS free for a second workgroup per CU, while the larger one does not.

Extend the 64-row tile to the (type, J) pairs where it measured faster on
gfx1151, and leave every other entry untouched. J=96 is deliberately excluded
because it did not benefit.

test-backend-ops perf on gfx1151, 100 MUL_MAT shapes over the affected types
(N in 48..512, M both padded and unpadded), 3 rounds: median +2.1%, best
+26.0%, no shape outside run-to-run noise. 5 MUL_MAT_ID shapes: median +8.0%.

Assisted-by: Claude Opus 5