Comment # 24 on bug 59982 from Alex Deucher

If the card is not posted by the sbios, the display hardware is disabled until
the driver attempts to initialize it.  The display controller enable bit is bit
0 of CRTC_CONTROL (0x6e70 + crtc_offset).  The DAC enable bit is bit 0 of
DAC_ENABLE (0x6790).