iommu: arm-smmu: prevent duplicate linear mapping

iommu: arm-smmu: prevent duplicate linear mapping

Display is requesting same linear mapping multiple times.
Adding variable in iommu_linear_map to track the mapping and
return if it is already mapped.

Bug 200300054

Change-Id: If4d9451c5c0b8d1136951aacdf7a5fdc0c4ad660
Signed-off-by: Pritesh Raithatha <praithatha@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/1516579
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>