add shapes for fill benchmark (#28966)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28966
as title
Test Plan:
```
buck run mode/opt //caffe2/benchmarks/operator_benchmark/pt:fill_test
# ----------------------------------------
# PyTorch/Caffe2 Operator Micro-benchmarks
# ----------------------------------------
# Tag : short
# Benchmarking PyTorch: fill_
# Mode: Eager
# Name: fill__N1024_cpu_dtypetorch.int32
# Input: N: 1024, device: cpu, dtype: torch.int32
Forward Execution Time (us) : 2.008
Reviewed By: hl475
Differential Revision: D18241521
fbshipit-source-id: 6eb6e1ab7e8a2f461c6fc537f5bb971d12f594c3
