spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

LinuxKPI: Add sort() wrapper.

swap parameter is not supported as it is rarely used in Linux kernel
and its implementation will add some preprocessor spaghetti to qsort.

Required by drm-kmod.

MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D33675