linuxkpi: Add trylock_page and unlock_page
Simple wrapper around vm_page_trylock and vm_page_unlock.
Reviewed by: hselasky
Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D36019
(cherry picked from commit d1c3cfd79da148755ef0fa51f65cd8d0d64b9a88)