Add fbgemm split_embedding_table benchmark
Summary:
Add the nbit_device test from fbgemm split_embedding_table benchmark
Source: https://www.internalfb.com/code/fbsource/fbcode/deeplearning/fbgemm/fbgemm_gpu/bench/split_table_batched_embeddings_benchmark.py
Reviewed By: int3
Differential Revision: D61215046
fbshipit-source-id: cb48557ff5163dd10a84534b0360bfade7f8988c
