unify gather benchmark (#28895)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28895
as title
Test Plan:
```
buck run mode/opt //caffe2/benchmarks/operator_benchmark/pt:conv_test
# ----------------------------------------
# PyTorch/Caffe2 Operator Micro-benchmarks
# ----------------------------------------
# Tag : short
# Benchmarking PyTorch: Conv1d
# Mode: Eager
# Name: Conv1d_in_c256_out_c256_kernel3_stride1_N1_L64_cpu
# Input: in_c: 256, out_c: 256, kernel: 3, stride: 1, N: 1, L: 64, device: cpu
Forward Execution Time (us) : 208.936
Reviewed By: hl475
Differential Revision: D18227757
fbshipit-source-id: 493dd81108848fe3d48fb5ad940eb6aef84b639c
