Summary

Two fixes for Cirrus onboard video:

• Revert to the old VBIOS loading behavior for the HP Vectra 486VL and Siemens-Nixdorf D824 machines resolving issues with the Windows 3.1 drivers
• Give the HP Vectra 486VL the correct ISA CL-GD5426 onboard video (instead of the 5428)

Checklist

• Closes Integrated Cirrus CL‑GD5428 Display Adapter Crashes on Boot in Windows 3.1 (HP Vectra 486VL / Siemens‑Nixdorf D824 / Alaris Cobalt LXP) #6820
• I have tested my changes locally and validated that the functionality works as intended
• I have discussed this with core contributors already
• This pull request requires changes to the ROM set
  • I have opened a roms pull request - https://github.com/86Box/roms/pull/changeme/
• This pull request requires changes to the asset set
  • I have opened an assets pull request - https://github.com/86Box/assets/pull/changeme/

References

Provide links to datasheets or other documentation that helped you implement this pull request.
TheRetroWeb page for the Vectra 486VL: https://theretroweb.com/motherboards/s/hp-vectra-486vl-pc-series-d3021,d3025