Use native fp8 format on MI300X

[HaiShaw]

Motivation

Use natively support e5m2 format on MI300X, so HW accelerated conversion can kick in.

Modifications

On none MI GPUs, or none native FP8 supported MI GPUs, no perf difference (as all done in torch emulation).

Checklist

• [+] Format your code according to the Contributor Guide.
• [+] Add unit tests as outlined in the Contributor Guide.
• [+] Update documentation as needed, including docstrings or example tutorials.