Since we want the SW INT to go off as soon as possible, write the
extra bits that will turn off the ITR wait for the interrupt.

Change-ID: I6d5382ba60840fa32abb7dea17c839eb4b5f68f7
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>