EBX: Contains the VM handle (always the currently executing VM).
EBP: Points to the Windows VM's Client Registers.
Save everything that you use. No values or flags need to be returned.
This call is very similar to PRE_HIRES_TO_VGA in that it allows the mini-VDD to modify port trapping, set flags, etc. in preparation for the mode change into the VESA/hi-res mode. In fact, the S3 example mini-VDD dispatches this call to the exact same routine as PRE_HIRES_TO_VGA.