linuxkpi: Add try_cmpxchg and atomic_try_cmpxchg
Needed by drm-kmod
Obtain from: drm-kmod
Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D36015
(cherry picked from commit 39da3678b1ce2d4fac300e022e544b1db5c117c0)