iommu/tegra: smmu: Fix race condition in writing PTC registers

iommu/tegra: smmu: Fix race condition in writing PTC registers

Fix race condition in programming PTC flush registers.
This race condition results in PTC flush not happening as intended and
can cause either SMMU fault or previous stale mapping access.

Bug 1625885
Bug 1603840

Change-Id: Ie94a8cfe947d8363a252f05dcd98fac10920586a
Signed-off-by: Krishna Reddy <vdumpa@nvidia.com>
Reviewed-on: http://git-master/r/724503
Reviewed-by: Hiroshi Doyu <hdoyu@nvidia.com>
Tested-by: Hiroshi Doyu <hdoyu@nvidia.com>
GVS: Gerrit_Virtual_Submit