Revert "drm/i915: Lock mode_config.mutex in intel_display_resume."

Revert "drm/i915: Lock mode_config.mutex in intel_display_resume."

This reverts commit f13bdc41007525d87f588745ebe59ca2ae396d26.

mode_config.mutex was originally added to fix WARNs in connector
functions, but now that atomic nonblocking modeset support is
included, we will likely never hold any any lock at all.

The WARN mentioned in commit f24dbd46fcc8aa68 ("drm/i915:
Pass atomic state to intel_audio_codec_enable, v2."), so it's
safe to revert this now.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1491312168-18147-1-git-send-email-maarten.lankhorst@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>