drm/fb-helper: don't disable everything in initial_config

This should be done in the drivers for two reasons:
- it gets in the way of fastboot efforts
- it links the fb helpers with the crtc helpers instead of going
  through the real interface vfuncs, forcing i915 to fake all the
  ->disable callbacks used by the crtc helper to avoid ugly Oopsen

v2: Resolve conflicts since drivers still call
drm_fb_helper_single_add_all_connectors.

Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_fb.c

@@ -258,6 +258,9 @@ void intel_fbdev_initial_config(struct drm_device *dev)
 {
 	drm_i915_private_t *dev_priv = dev->dev_private;
 
+	/* disable all the possible outputs/crtcs before entering KMS mode */
+	drm_helper_disable_unused_functions(dev);
+
 	/* Due to peculiar init order wrt to hpd handling this is separate. */
 	drm_fb_helper_initial_config(&dev_priv->fbdev->helper, 32);
 }