register and page register when carrying out 16-bit DMA? this change
updates the code to allow either one method that allows 128KB boundaries
for 16-bit DMA (which DOSBox has already been doing anyway) and the
other method that limits 16-bit DMA to 64KB boundaries but preserves all
bits of the page register (which is said to be the way PCI-based
motherboard do it). You can choose which one from dosbox.conf now, or
let DOSBox-X decide based on your hardware configuration (which is
currently based on whether or not the VM has PCI emulation enabled).
