dts: bindings: gpio: Add STEMMA-QT connector

Add a definition of a STEMMA QT connector to which I2C
devices can be connected.

Since STEMMA-QT does not specify uses other than I2C,
this is just a formal definition.
(It may be helpful when using this connector as a GPIO,
 which is not defined in STEMMA-QT)

Maybe in usual need to define i2c alias such like as,

```
stemma_qt_i2c: &i2c0 { }
```

Signed-off-by: TOKITA Hiroshi <[email protected]>
Co-authored-by: Benjamin Cabé <[email protected]>

Author: soburi

dts/bindings/gpio/stemma-qt-connector.yaml

@@ -0,0 +1,20 @@
+# Copyright (c) 2024 TOKITA Hiroshi
+# SPDX-License-Identifier: Apache-2.0
+
+description: |
+    STEMMA QT is a 1.0mm-JST-SH connector for I2C devices.
+    The pin assignments are as follows.
+
+        0  SCL
+        1  SDA
+        -  VCC (3-5V)
+        -  GND
+
+    STEMMA, Grove, Qwiic, and Gravity connectors are similar to this,
+    but the connector form and VCC voltage are different.
+    Please see
+    https://learn.adafruit.com/introducing-adafruit-stemma-qt/stemma-qt-comparison#quick-comparison-3035247
+
+compatible: "stemma-qt-connector"
+
+include: [gpio-nexus.yaml, base.yaml]