fix issue 3637: mstatus.SD stays clear when mstatus.VS is Dirty

[huntersubmit]

Fix issue 3637

issue: #3637

Summary

This PR fixes the computation of the mstatus.SD summary bit when the vector state (mstatus.VS) is Dirty.

Root cause analysis

The existing mstatus.SD logic only checked whether mstatus.XS or mstatus.FS was Dirty.

It did not include mstatus.VS, even though VS is another state-status field summarized by SD.

As a result, when VS became Dirty, SD remained clear unless XS or FS was also Dirty.

The surrounding configuration guard also covered only the supervisor and floating-point configuration flags.

It did not include CVA6Cfg.RVV, so a vector-enabled configuration was not independently sufficient to enable the summary-bit computation.

Fix

The mstatus.SD expression now includes (mstatus_d.vs == riscv::Dirty) alongside the existing XS and FS conditions.
The configuration guard also includes CVA6Cfg.RVV.

The computation uses the next-state value mstatus_d.vs, preserving the existing combinational update model and ensuring that SD is asserted in the same update in which vector state becomes Dirty.