radeonfb_scratch_test
static int radeonfb_scratch_test(struct radeonfb_softc *, int, uint32_t);
if (radeonfb_scratch_test(sc, RADEON_BIOS_0_SCRATCH, 0x55555555) ||
radeonfb_scratch_test(sc, RADEON_BIOS_0_SCRATCH, 0xaaaaaaaa)) {