LinuxKPI: Add xa_(un)lock_irq to linux/xarray.h

On FreeBSD they are equal to non-irq version.

Sponsored by: Serenity Cyber Security, LLC
Reviewed by: manu, bz
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D42803

(cherry picked from commit 66f9a98335dcc2a3c1eead0d80ccc9fee12bbb31)