LinuxKPI: add devm_kfree()

mt76 calls devm_kfree() directly, so alias it to our
lkpi_devm_kmalloc_release() function.

Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D44589

(cherry picked from commit 170c2e0e2bb1b2d9a7661ba729f8264381c9d9d7)