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/ast/ast_fb.c

@@ -40,6 +40,7 @@
 #include <drm/drmP.h>
 #include <drm/drm_crtc.h>
 #include <drm/drm_fb_helper.h>
+#include <drm/drm_crtc_helper.h>
 #include "ast_drv.h"
 
 static void ast_dirty_update(struct ast_fbdev *afbdev,
@@ -314,6 +315,10 @@ int ast_fbdev_init(struct drm_device *dev)
 	}
 
 	drm_fb_helper_single_add_all_connectors(&afbdev->helper);
+
+	/* disable all the possible outputs/crtcs before entering KMS mode */
+	drm_helper_disable_unused_functions(dev);
+
 	drm_fb_helper_initial_config(&afbdev->helper, 32);
 	return 0;
 }