i started getting this problem back with 1.4.3ish kernels really
but didnt decide to do anything about it till now.  booting a 
1.5 kernel on my q700 panics because it doesnt see my internal
video (i dont see an intvid0 config line during boot)

with a couple printf()'s i tracked this down to:

        case MACH_CLASSQ:
                /*
                 * Assume DAFB for all of these, unless we can't
                 * access the memory.
                 */
                base = DAFB_CONTROL_BASE;

                if (bus_space_map(oa->oa_tag, base, 0x1000, 0, &bsh))
                        return 0;

it seems the bus_space_map() fails and my intvid device isnt configured.
for the time being i an using a nubus video board.  any ideas anyone?