linuxkpi: Define xa_is_err(), xa_{store,erase}_irq() and xa_{,un}lock_irq*()

xa_is_err() is synonymous to IS_ERR().

Other introduced functions call their equivalent without the irq*
suffix.

Reviewed by: manu
Approved by: manu
Differential Revision: https://reviews.freebsd.org/D38534

(cherry picked from commit 5542309ec6eba3af9e26c50acd654de462181b8e)