iommu/tegra-smmu: Split smmu_flush_ptc()

smmu_flush_ptc() is used in two modes: one is to flush an individual
entry, the other is to flush all entries.  We know at the call site
which we require.  Split the function into smmu_flush_ptc_all() and
smmu_flush_ptc().

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Thierry Reding <treding@nvidia.com>