qat: update API files to use SPDX identifier
API files are updated to have SPDX identifier and remove
longer form of license to ensure consistency with the
license format across all files.
Reviewed by: markj, ziaee
MFC after: 2 weeks
Sponsored by: Intel Corporation
Differential Revision: https://reviews.freebsd.org/D50379
(cherry picked from commit 2542189532b3025577fa4e782904494f3587008b)