linuxkpi: Add llnode member in struct irq_work
This was added in Linux v5.8 and started to be used in drm code in v5.9
MFC after: 1 week
Sponsored by: Beckhoff Automation GmbH & Co. KG
(cherry picked from commit 17ee6aca65c8dfb5f041b3229655ce12b0f37372)