iommu/amd: Tell kmemleak about the irq_remap_table

This will get rid of a lot false positives caused by kmemleak being
unaware of the irq_remap_table. Based on a suggestion from Catalin Marinas.

Signed-off-by: Lucas Stach <dev@lynxeye.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>