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 ea49c9acf2db7082f0406bb3a570cc6bad37082b.

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 bbf35e9defb9a6d1 ("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>