drm/i915: Move unload time GTT, MSI IRQ cleanup later

Move the GTT,MSI IRQ cleanup later so that it matches their
corresponding init order. Also fix the order of these calls wrt. each
other to match their 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/1458128348-15730-13-git-send-email-imre.deak@intel.com