Implement cusparse Descriptor class and clean up cusparse code (#37389)
Summary:
Add cusparse Descriptor class. Add cusparse Generic API wrapper. Clean up current cuda sparse code.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37389
Differential Revision: D21302691
Pulled By: ezyang
fbshipit-source-id: ecbb4063466c616eebfe681f1622724692be505c
