[ROCm] restore MIOpen benchmark flag default to true (#82656)
### Description
PR https://github.com/pytorch/pytorch/pull/77438 allowed MIOpen to support the benchmark flag. Previously, the benchmark flag was ignored by MIOpen such that benchmarking was always turned on. This commit restores the behavior that MIOpen benchmarking is by default turned on.
### Testing
CI unit tests cover this capability. Torchvision models demonstrate the performance delta.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/82656
Approved by: https://github.com/ngimel
