Explain why we cannot remove this code, even though it works differently
than any of our other interrupt cause handling code.

Change-ID: Ie66203bd037a466066036611c31d44f759ec5176
Signed-off-by: NMitch Williams <mitch.a.williams@intel.com>
Tested-by: NAndrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>