Trackball rewrite (#600)

- Implement generic trackball settings
- Refactor T-Deck trackball driver into generic driver at `Drivers/gpio-trackball-module`
- Automatically bind/unbind trackball devices with LVGL
- Automatically load settings for trackball devices on boot

Drivers/gpio-trackball-module/README.md

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+# GPIO Trackball
+
+Kernel driver for a 5-way GPIO trackball (4 direction pins + a click button), exposing a
+`TRACKBALL_TYPE` device (`tactility/drivers/trackball.h`).
+
+Devicetree binding: `tactility,gpio-trackball` (see `bindings/tactility,gpio-trackball.yaml`).
+
+Each direction pin is wired to a falling-edge interrupt that accumulates a signed delta;
+the click pin is active-low and read on any edge. `read_delta()` drains and resets the
+accumulated delta on each call.
+
+## Example
+
+```dts
+trackball {
+    compatible = "tactility,gpio-trackball";
+    pin-right = <&gpio0 1 GPIO_FLAG_NONE>;
+    pin-up = <&gpio0 2 GPIO_FLAG_NONE>;
+    pin-left = <&gpio0 3 GPIO_FLAG_NONE>;
+    pin-down = <&gpio0 4 GPIO_FLAG_NONE>;
+    pin-click = <&gpio0 5 GPIO_FLAG_NONE>;
+};
+```
+
+## License
+
+[Apache License Version 2.0](LICENSE-Apache-2.0.md)