drm/i915: Reduce INTEL_DISPLAY_ENABLED to just removing the outputs

drm/i915: Reduce INTEL_DISPLAY_ENABLED to just removing the outputs

Having a mode where the display hardware is present but we try
to pretend it isn't just leads to massive headaches when trying
to reason what the fallout might be from skipping some random
bits of programming.

Let's just neuter INTEL_DISPLAY_ENABLED so that we treat the
hardware as fully present, except we just don't register any
outputs. That's still rather sketchy if the outputs are already
enabled when the driver is loaded. I think the simplest solution
would be to probe everything as normal and just return
disconnected" from all .detect() hooks. That would avoid anything
automagically enabling those outputs, but the driver could then
shut things down using the normal codepaths.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200909213824.12390-1-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>