drm/i915/skl: Fix power domain suspend sequence

During system suspend we need to first disable power wells then
unitialize the display core. In case power well support is disabled we
did this in the wrong order, so fix this up.

Fixes: d314cd43 ("drm/i915: fix handling of the disable_power_well module option")
CC: stable@vger.kernel.org
CC: Patrik Jakobsson <patrik.jakobsson@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Patrik Jakobsson <patrik.jakobsson@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1456778945-5411-1-git-send-email-imre.deak@intel.com