drm/i915: Call uncore_suspend before platform suspend handlers

Quoting Ville: "the forcewake timer might still be active until the uncore
suspend, and having active forcewakes while we've already told the GT wake
stuff to stop acting normally doesn't seem quite right to me."

Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Suggested-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171114135518.15981-3-hdegoede@redhat.com