dt-bindings: memory: tegra: Add Tegra234 support

Document the variant of the memory controller and external memory
controllers found on Tegra234 and add some memory client and SMMU
stream ID definitions for use in device tree files.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>