LinuxKPI: cleanup: implement __free() and DEFINE_FREE(); use for kfree()
A wifi driver update needs this.
Sponsored by: The FreeBSD Foundation (initially)
Reviewed by: dumbbell
Differential Revision: https://reviews.freebsd.org/D52075
(cherry picked from commit 39e9290d890b2aa07b68f2fe956b96e5df9a1da2)