dt-bindings: display: add EDT ET035012DM6 display description

Add support for the ET035012DM6 3.5" QVGA TFT LCD panel. The datasheet
can be retrieved online:

https://www.glynshop.com/erp/owweb/Daten/DSS/EDT/Products/ \
Specifications/Active%20Displays/ET035012DM6.pdf
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190416101630.3482-1-m.felsch@pengutronix.de

Documentation/devicetree/bindings/display/panel/edt,et-series.txt

@@ -6,6 +6,14 @@ Display bindings for EDT Display Technology Corp. Displays which are
 compatible with the simple-panel binding, which is specified in
 simple-panel.txt
 
+3,5" QVGA TFT Panels
+--------------------
++-----------------+---------------------+-------------------------------------+
+| Identifier      | compatbile          | description                         |
++=================+=====================+=====================================+
+| ET035012DM6     | edt,et035012dm6     | 3.5" QVGA TFT LCD panel             |
++-----------------+---------------------+-------------------------------------+
+
 4,3" WVGA TFT Panels
 --------------------