[CK][CK_TILE] Fix FMHA codegen group mode dispatcher for fwd & bwd

[arthurliu1998]

Motivation

FMHA codegen had incorrect dispatch behavior in group mode. Two root causes:

1. Wrong field names in dispatch conditions — Used batch-mode fields (seqlen_q, seqlen_k) instead of group-mode fields (max_seqlen_q, max_seqlen_k), causing wrong kernel selection at runtime on gfx950.
2. Missing kernel variants — Group mode was overly filtered out from smaller-tile specializations (bwd) and lacked spatial-padding pipeline variants on gfx950 (fwd).

gfx942 don't support trload pipeline.

Technical Details

fmha_bwd.py:

• max_seq_q_cond and extra_cond now emit t.max_seqlen_q / t.max_seqlen_k for group mode.
• Relaxed kernel filtering: group mode no longer skips tiles with max_seq_q != 0.

fmha_fwd.py:

• get_bm0_cond emits a.max_seqlen_q for group mode tile-size dispatch.
• Added two qr_async_trload pipeline variants with spatial padding for gfx950 group mode.

Test Plan

Triggering AITER CI job:

Test Result

Submission Checklist

• Look over the contributing guidelines at

https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.