drm/i915/display: Go softly softly on initial modeset failure

Reduce the module/device probe error into a mere debug to hide issues
where the initial modeset is failing (after lies told by hw probe) and
the system hangs with a livelock in cleaning up the failed commit.

Reported-by: H.J. Lu <hjl.tools@gmail.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=210619
Fixes: b3bf99d ("drm/i915/display: Defer initial modeset until after GGTT is initialised")
Fixes: ccc9e67 ("drm/i915/display: Defer initial modeset until after GGTT is initialised")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: H.J. Lu <hjl.tools@gmail.com>
Cc: Dave Airlie <airlied@redhat.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201210230741.17140-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/display/intel_display.c

@@ -18040,7 +18040,7 @@ int intel_modeset_init(struct drm_i915_private *i915)
 	 */
 	ret = intel_initial_commit(&i915->drm);
 	if (ret)
-		return ret;
+		drm_dbg_kms(&i915->drm, "Initial modeset failed, %d\n", ret);
 
 	intel_overlay_setup(i915);