iommu/vtd: Cleanup dma_remapping.h header

Commit e61d98d8

 ("x64, x2apic/intr-remap: Intel vt-d, IOMMU
code reorganization") moved dma_remapping.h from drivers/pci/ to
current place. It is entirely VT-d specific, but uses a generic
name. This merges dma_remapping.h with include/linux/intel-iommu.h
and removes dma_remapping.h as the result.

Cc: Ashok Raj <ashok.raj@intel.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Sohil Mehta <sohil.mehta@intel.com>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Liu, Yi L <yi.l.liu@intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>