Add the clear_pxe AdminQ API call.

Change-ID: Ia770ff3404971bb3889b53a39c3a7bfaf3f4d399
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>