iommu/tegra: smmu: Remove unnecessary PTC/TLB flush all

smmu_flush_regs() does TLB/PTC flush all when freeing a second level
page table. This isn't necessay at all since each pte entry has been
already maintained by address in the above flush_ptc_and_tlb().

Signed-off-by: Hiroshi Doyu <hdoyu@nvidia.com>
Signed-off-by: Joerg Roedel <joro@8bytes.org>