Enable stereoscopic output for HDMI and DisplayPort connectors on
NV50+ (G80+) hardware.  We do not enable stereoscopy on older
hardware in case there is some older board that still has HDMI
output but for which we have no logic for setting the Vendor
InfoFrame.

With this, I get an obvious 3D output when using the "testdisplay"
program from intel-gpu-tools with the "-3" parameter and outputting
to a 3D-capable HDMI display, for all available 3D modes (be they
TB, SBSH, or FP) on all four G80+ DISPs.
Signed-off-by: Alastair Bridgewater <alastair.bridgewater@gmail.com>