drm/i915: Move load time shrinker registration later

According to the new init phases scheme we should register the driver
with frameworks/userspace only one the device is setup fully. So move
the shrinker registration later accordingly.

Also fix the shrinker unregistration order wrt. the acpi unregistration
to fix the corresponding init order.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1458128348-15730-10-git-send-email-imre.deak@intel.com