Refactor1: Move files to fmha/ folder

[danthe3rd]

Stack from ghstack (oldest at bottom):

• Refactor8: Reapply changes from Artem #571
• Refactor7: Restore dropout #570
• TritonFlash: Enable only on Sm80 #568
• Refactor5: Generic way of registring operators for xformers.info #561
• Refactor4: Split fw/bw operators #560
• Refactor3: Embed flash's PY files as xformers._flash_attn #557
• Update FlashAttention #495
• -> Refactor1: Move files to fmha/ folder #555
• Fix CI after torchmetrics update #567

[codecov-commenter]

Codecov Report

Base: 89.08% // Head: 89.08% // No change to project coverage 👍

Coverage data is based on head (e657ded) compared to base (e657ded).
Patch has no changes to coverable lines.

❗ Current head e657ded differs from pull request most recent head a3f4ab8. Consider uploading reports for the commit a3f4ab8 to get more accurate results

Additional details and impacted files

@@                  Coverage Diff                  @@
##           gh/danthe3rd/56/base     #555   +/-   ##
=====================================================
  Coverage                 89.08%   89.08%           
=====================================================
  Files                        80       80           
  Lines                      4929     4929           
=====================================================
  Hits                       4391     4391           
  Misses                      538      538           

Flag	Coverage Δ
Python	89.08% <0.00%> (ø)

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[fmassa]

Thanks!