custom gpu option

[dipanban]

This change resolves the issue of loading the pre-trained model into any other gpu for systems with multiple multiple gpu.
setting visible device is a bypass but I needed to use two gpus in parallel for modelling and reaction mapping in a common environment, so this feature seemed useful. Thanks. Please let me know about your thoughts and apologies if anything is done inappropriately as this is my first PR.
signed-off by : Dipan Banik dipanbanik104@gmail.com

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[cla-bot]

Thank you for your pull request and welcome to our community. We could not parse the GitHub identity of the following contributors: dipan.banik.
This is most likely caused by a git client misconfiguration; please make sure to:

1. check if your git client is configured with an email to sign commits git config --list | grep email
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