iommu/vt-d: Remove unnecessary exported symbol

The exported symbol intel_iommu_gfx_mapped is not used anywhere in the
tree. Remove it to avoid dead code.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Steve Wahl <steve.wahl@hpe.com>
Link: https://lore.kernel.org/r/20220514014322.2927339-4-baolu.lu@linux.intel.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>