dt-bindings: display: Add ETM0430G0DH6 bindings

Document the Emerging Display Technology Corp. (EDT) ETM0430G0DH6
display, which is a 480x272 4.3" TFT display.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Jan Tuerk <jan.tuerk@emtrion.com>
Cc: Thierry Reding <treding@nvidia.com>
Cc: devicetree@vger.kernel.org
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190219140438.17063-1-marex@denx.de