x86: pci-dma_64.c: cleanups

This patch contains the following cleanups:
- make the needlessly global iommu_setup() static
- remove the unused EXPORT_SYMBOL(iommu_merge)

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>