drm/i915: Use gen8_gt_irq_reset() in cherryview_irq_uninstall()

Replace the hand rolled macros with gen8_gt_irq_reset() and
GEN5_IRQ_RESET() in cherryview_irq_uninstall().

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>