fix(csr): recompute status sd from next-state fs/xs

[jf-cc727]

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This PR fixes a stale sd recomputation issue in the CSR status path.

It recomputes mstatus.sd from mstatus_d.{xs,fs} and vsstatus.sd from vsstatus_d.{xs,fs}, instead of using the old registered _q state. This keeps sd consistent with same-cycle updates that already make fs or xs dirty.

Related issue: #3460

Why this change is needed:

sd is a summary bit derived from the dirty state of fs/xs. In the current implementation, fs can already be updated to Dirty in the next-state logic, while sd is still recomputed from the previous registered state. This creates a one-cycle inconsistency where the visible fs state has advanced but sd still reflects the old value.

Validation:

• validated with the test reproducer
• the reproducer passes with this patch applied (tohost = 0)

Current limitation:

This is a narrow consistency fix for sd recomputation and does not otherwise change CSR status semantics.

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