Hi,
Hopefully Gerd has experience using bochs_drm with other non-x86 systems and can comment further.
Just pushed to drm-misc-next, fix is correct. bochs video memory is a pci bar, and the framebuffer is stored there.
Using sys instead of cfb is probably a leftover from cirrus, where the framebuffer actually in a shadow copy in system ram, due to the low amout of (pci) video memory.
cheers, Gerd