iommu/tegra-smmu: Staticize tegra_smmu_pm_ops

'tegra_smmu_pm_ops' is used only in this file. Make it static.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Hiroshi Doyu <hdoyu@nvidia.com>
Signed-off-by: Joerg Roedel <joro@8bytes.org>