Revert "drm/i915/bxt: Disable device ready before shutdown command"

This reverts commit bbdf0b2f ("drm/i915/bxt: Disable device ready
before shutdown command").

Disable device ready before shutdown command was added previously to
avoid a split screen issue seen on dual link DSI panels. As of now, dual
link is not supported and will need some rework in the upstream
code. For single link DSI panels, the change is not required. This will
cause failure in sending SHUTDOWN packet during disable. Hence reverting
the change. Will handle the change as part of dual link enabling in
upstream.

Fixes: bbdf0b2f

 ("drm/i915/bxt: Disable device ready before shutdown command")
Cc: <stable@vger.kernel.org> # v4.12+
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Vidya Srinivas <vidya.srinivas@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1504604671-17237-1-git-send-email-vidya.srinivas@intel.com
(cherry picked from commit 33c8d887

)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>