#1411 OLDER_GPUS.md: the P100 row now has a measurement (2x P100, IQ3_S)

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Follow-up to #1157. The Support matrix still said 'not measured' for the Tesla P100; #1157 supplied a 2x P100 IQ3_S report, so this fills the row in the same style as the P40 and V100 rows: prompt 526-532 tok/s, decode 28-32 tok/s at 128K prompt tokens, 3 of 3 needle checks at 122K, linking bench/results/2026-10-06-community-2x-p100/. Kept separate from the results PR so reviewers can assess the measurements directly, as COMMUNITY_BENCHMARKS.md asks.