memory: tegra: Add software memory clients in Tegra234

Add dummy memory controller clients to represent CPU clusters. They will
be used by the CPUFREQ driver to scale DRAM FREQ with the CPU FREQ.

Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>