[Intel-gfx] Supporting fused display configurations v5

[Damien Lespiau]

Follow up of v4:
  http://lists.freedesktop.org/archives/intel-gfx/2014-January/037913.html

The major changes are:
  - we try to be cunning on CPT/PPT and look at the fuses lock bit of
    SFUSE_STRAP to detect if PCH display reads are being dropped
  - we provide a module parameter to forcefully disable display. This can help
    if we don't manage to detect the display is fused off.
  - INTEL_INFO() is still in use as it'd make compiling parts of the driver out
    easier (as Daniel showed)

-- 
Damien