iommu/tegra-smmu: Move flush_dcache to tegra-smmu.c

Drivers should not be using __cpuc_* functions nor outer_cache_flush()
directly.  This change partly cleans up tegra-smmu.c.

The only difference between cache handling of the tegra variants is
Denver, which omits the call to outer_cache_flush().  This is due to
Denver being an ARM64 CPU, and the ARM64 architecture does not provide
this function.  (This, in itself, is a good reason why these should not
be used.)

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
[treding@nvidia.com: fix build failure on 64-bit ARM]
Signed-off-by: Thierry Reding <treding@nvidia.com>