linuxkpi: Add cond_resched_lock

If we need to resched it takes the lock, resched, release the lock
and returns 1, otherwise simply returns 0.

Needed by drm v5.9

MFC after: 1 month
Reviewed by: hselasky
Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D34620