Enable hipBLASLt as an optional backend for MIOpen GEMM kernels

[BrianHarrisonAMD]

1. Description:

Enable hipBLASLt as an optional backend for MIOpen GEMM kernels.

For this first implementation we are proposing:

• Enable hipBLASLt as an option when using the environment overrides MIOPEN_GEMM_ENFORCE_BACKEND == 5

2. Value & Motivation:

• hipBLASLt is a new GEMM backend that is available for use, and we want to enable this backend as an option within MIOpen.
• Adding support for this backend within MIOpen will give more options for selecting the optimal solver.
• Starting with a limited roll out will allow for testing & benchmarking.

3. Any additional information:

• This is intended to be a minimal & focused implementation to enable using the hipBLASLt backend within MIOpen.

[BrianHarrisonAMD]

Note: Associated draft PR here #3030

[BrianHarrisonAMD]

In PR #3030 we discussed, "Use hipBLASLt as the backend GEMM kernels for RNNs on targeted hardware using half precision", and decided to instead have it only accessible via the environment variable, "MIOPEN_GEMM_ENFORCE_BACKEND=5" with this first limited rollout.