PR #12193: [GPU] Move workspace to be the last operand of cuDNN FMHA.
PR #12193: [GPU] Move workspace to be the last operand of cuDNN FMHA.

Imported from GitHub PR https://github.com/openxla/xla/pull/12193

This will enable a large simplification in a next PR.
Copybara import of the project:

--
ad747544396d4920e60946d7a0f00300f47e07d2 by Ilia Sergachev <isergachev@nvidia.com>:

[GPU] Move workspace to be the last operand of cuDNN FMHA.

Merging this change closes #12193

FUTURE_COPYBARA_INTEGRATE_REVIEW=https://github.com/openxla/xla/pull/12193 from openxla:move_fmha_workspace ad747544396d4920e60946d7a0f00300f47e07d2
