LinuxKPI: add cleanup.h to mutex.h

Some code relies on header pollution (or self-sustainability).
Add cleanup.h to mutex.h as that is one case it seems to be used with.

Sponsored by: The FreeBSD Foundation
Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D50001

(cherry picked from commit 059136a95aca2e550b62ef40ab25a184d8141124)