[Minor] Expose bias options for both MLP and FusedMLP, use same defaults

[blefaudeux]

What does this PR do?

Looking into #219 exposed that MLP and FusedMLP were not using the same defaults (bias and no bias respectively), and that Timm defaulted to using a bias. This PR

• exposes the bias flag
• uses the same default for both MLP and FusedMLP
• use default bias=True so that it's the same as Timm

Before submitting

• Did you have fun?
  • Make sure you had fun coding 🙃
• Did you read the contributor guideline?
• Was this discussed/approved via a Github issue? (no need for typos, doc improvements)
  • N/A
• Did you make sure to update the docs?
  • N/A
• Did you write any new necessary tests?
  • N/A
• Did you update the changelog? (if needed)
  • N/A

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

[blefaudeux]

cc @jramapuram, but this is not the reason for your issue, since you were seeing the same number of parameters

[codecov-commenter]

Codecov Report

Merging #220 (2926d46) into main (a65c243) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #220   +/-   ##
=======================================
  Coverage   91.72%   91.72%           
=======================================
  Files          60       60           
  Lines        3214     3214           
=======================================
  Hits         2948     2948           
  Misses        266      266           

Flag	Coverage Δ
Python	91.72% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
xformers/components/feedforward/fused_mlp.py	91.30% <ø> (ø)
xformers/components/feedforward/mlp.py	100.00% <ø> (ø)
xformers/triton/layer_norm.py	76.92% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a65c243...2926d46. Read the comment docs.

[blefaudeux]

Guessing that this is small enough to land, not changing anything really deep, exposing existing params and aligning defaults