drm/i915: Move load time IRQ SW init earlier

Most of the IRQ init is setting up hooks so move that part earlier.
Leave the pm_qos_add_request() call in place.

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/1458128348-15730-4-git-send-email-imre.deak@intel.com