Merge straggling core drm patches.

* 'topic/core-stuff' of git://git.freedesktop.org/git/drm-intel:
  drm: Fix use-after-free in the shadow-attache exit code
  drm/fb-helper: Do the 'max_conn_count' zero check
  drm: Check if the allocation has succeeded before dereferencing newmode
  drm/fb-helper: Use drm_fb_helper_restore_fbdev_mode() in drm_fb_helper_set_par()
  drm/edid: request HDMI underscan by default