Skip test_quantized_nn_mods tests if theres no FBGEMM
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/24302
Test Plan: Imported from OSS
Differential Revision: D16800352
Pulled By: jamesr66a
fbshipit-source-id: 56650d8c937afca77005ad39a5bc38ebd6e71414
