dt-bindings: iio: light: Added AMS tsl2591 device tree binding

Device tree binding for AMS/TAOS tsl2591 ambient light sensor.

This driver supports configuration via device tree and sysfs.
Supported channels for raw infrared light intensity,
raw combined light intensity and illuminance in lux.
The driver additionally supports iio events on lower and
upper thresholds.

This is a very-high sensitivity light-to-digital converter that
transforms light intensity into a digital signal.
Signed-off-by: Joe Sandom <joe.g.sandom@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20210421221330.17007-2-joe.g.sandom@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/light/amstaos,tsl2591.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/light/amstaos,tsl2591.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: AMS/TAOS TSL2591 Ambient Light Sensor (ALS)
+
+maintainers:
+  - Joe Sandom <joe.g.sandom@gmail.com>
+
+description: |
+  AMS/TAOS TSL2591 is a very-high sensitivity
+  light-to-digital converter that transforms light intensity into a digital
+  signal.
+
+properties:
+  compatible:
+    const: amstaos,tsl2591
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+    description:
+      Interrupt (INT:Pin 2) Active low. Should be set to IRQ_TYPE_EDGE_FALLING.
+      interrupt is used to detect if the light intensity has fallen below
+      or reached above the configured threshold values.
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/irq.h>
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        tsl2591@29 {
+            compatible = "amstaos,tsl2591";
+            reg = <0x29>;
+            interrupts = <20 IRQ_TYPE_EDGE_FALLING>;
+       };
+    };
+...