* Update fMHA kernels
Upstream recent changes to fMHA that we did in xFormers.
Previous version in CUTLASS: facebookresearch/xformers@b6be33a
Updating to: facebookresearch/xformers@55a4798
* minor changes
* make var work
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Co-authored-by: danthe3rd <danthe3rd>
Co-authored-by: Haicheng Wu <haichengw@nvidia.com>