x86, irq: Move irq_remapped out of x86 core code

The irq_remapped function is only used in IOMMU code after
the last patch. So move its definition there too.

Signed-off-by: Joerg Roedel <joro@8bytes.org>
Acked-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>