assign gpu with arguments

[pthavarasa]

Describe the question

if i enable gpu args.enable_cuda=True by default it use 'cuda:0' but i have multiple gpu on my pc
so i think we can make an argument or environment variable CUDA_VISIBLE_DEVICES to chose manually.

My background

Have I read the README.md file?

• yes

Have I searched for similar questions from closed issues?

• yes

Have I tried to find the answers in the paper Fully Supervised Speaker Diarization?

• yes

Have I tried to find the answers in the reference Speaker Diarization with LSTM?

• yes

Have I tried to find the answers in the reference Generalized End-to-End Loss for Speaker Verification?

• yes