devicetree: add documentation for MAX30102 oximeter

Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NMatt Ranostay <matt@ranostay.consulting>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/health/max30102.txt

+Maxim MAX30102 heart rate and pulse oximeter sensor
+
+* https://datasheets.maximintegrated.com/en/ds/MAX30102.pdf
+
+Required properties:
+  - compatible: must be "maxim,max30102"
+  - reg: the I2C address of the sensor
+  - interrupt-parent: should be the phandle for the interrupt controller
+  - interrupts: the sole interrupt generated by the device
+
+  Refer to interrupt-controller/interrupts.txt for generic
+  interrupt client node bindings.
+
+Optional properties:
+  - maxim,red-led-current-microamp: configuration for RED LED current
+  - maxim,ir-led-current-microamp: configuration for IR LED current
+
+    Note that each step is approximately 200 microamps, ranging from 0 uA to
+    50800 uA.
+
+Example:
+
+max30100@57 {
+	compatible = "maxim,max30102";
+	reg = <0x57>;
+	maxim,red-led-current-microamp = <7000>;
+	maxim,ir-led-current-microamp = <7000>;
+	interrupt-parent = <&gpio1>;
+	interrupts = <16 2>;
+};