[ROCM] enable miopen for rnn f16 (#52475)
Summary:
This PR enables using MIOpen for RNN FP16 on ROCM.
It does this by altering use_miopen to allow fp16. In the special case where LSTMs use projections we use the default implementation, as it is not implemented in MIOpen at this time. We do send out a warning once to let the user know.
We then remove the various asserts that are no longer necessary since we handle the case.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/52475
Reviewed By: H-Huang
Differential Revision: D27449150
Pulled By: malfet
fbshipit-source-id: 06499adb94f28d4aad73fa52890d6ba361937ea6
