dt-bindings: memory: tegra20: emc: Document new interconnect property

External Memory Controller is interconnected with memory controller and
with external memory. Document new interconnect property which turns EMC
into interconnect provider.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201104164923.21238-8-digetx@gmail.com


Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>