drm/i915/skl: Don't disable misc IO power well during display uninit

Bspec requires leaving the misc IO power well enabled during display
uninit, so align the code accordingly.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1498750622-14023-3-git-send-email-imre.deak@intel.com