[XLA:GPU] Re-populate `gpu_compiler_test_autotune_db.textproto` appropriately.
[XLA:GPU] Re-populate `gpu_compiler_test_autotune_db.textproto` appropriately.

This fixes `GpuCompilerTest.GemmFusionIsNoOpWhenGemmFusionAutotunerFallsBackToCublas`.
We also enforce a check that all the autotuning results are pre-loaded from
`gpu_compiler_test_autotune_db.textproto`, which will give us a better error
message (and a deterministic failure) should such an issue come up again.

We also disable the test pre-Ampere, since we did not generate autotuning results
below sm80.
