dt-bindings: memory: tegra20: emc: Convert to schema

Convert Tegra20 External Memory Controller binding to schema.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Link: https://lore.kernel.org/r/20210510212320.3255-1-digetx@gmail.com


Signed-off-by: Rob Herring <robh@kernel.org>