iommu/vt-d: Set IRTA in intel_setup_irq_remapping

This way we can give the hardware the new IR table right
after it has been allocated and initialized.

Tested-by: ZhenHua Li <zhen-hual@hp.com>
Tested-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>