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/mgag200/mgag200_fb.c

@@ -13,6 +13,7 @@
 #include <linux/module.h>
 #include <drm/drmP.h>
 #include <drm/drm_fb_helper.h>
+#include <drm/drm_crtc_helper.h>
 
 #include <linux/fb.h>
 
@@ -278,6 +279,10 @@ int mgag200_fbdev_init(struct mga_device *mdev)
 		return ret;
 	}
 	drm_fb_helper_single_add_all_connectors(&mfbdev->helper);
+
+	/* disable all the possible outputs/crtcs before entering KMS mode */
+	drm_helper_disable_unused_functions(mdev->dev);
+
 	drm_fb_helper_initial_config(&mfbdev->helper, 32);
 
 	return 0;