Are we talking something other than drivers/gpu/drm/pl111/ ?
This is the older fbdev driver that used to live at drivers/video/fbdev/amba-clcd.c but was removed in Linux 6.8. I actually haven't tested if the DRM driver works since it isn't really relevant to my use case.
Generally QEMU goes with "behave as the hardware does", though
for these old boards that gets kind of tricky. My gut feeling is
"this is a guest kernel bug that should be fixed in the guest
kernel".
I guess it was a long shot getting some sort of command line switch accepted for probably just one user. I'm guessing the kernel driver only ever really got tested with vexpress boards or something, so maybe it never even worked on real versatilepb hardware. The fact that the switch is there at all though suggests someone at one point ran it on something with a PL110. I guess there's not much to be done but create my own private kernel patchset.