Summary

This PR makes the following changes to the IBM PS/1 XTA controller:

• Clear Interrupt Request bit in Attachment Status Register after reading Interrupt Status Register per the manual
• Raise interrupt only after all Command Control Block bytes are received, fixes IBM OS/2 1.1-1.3 not recognizing any partition on the disk (previously only IBM OS/2 1.30.2 works)

Checklist

• Closes #xxx
• 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

IBM PS/1 Technical Reference Section 8 Drives: https://www.mediafire.com/download/ecok59mrc8sclzb/Section_8._Drives.pdf