dt-bindings: Add documentation for qbt_handler

Qualcomm Technologies, Inc. QBT_HANDLER Specific Bindings

QBT is a fingerprint sensor ASIC capable of performing fingerprint image scans

and detecting finger presence on the sensor using programmable firmware.

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Required Node Structure

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- compatible

  Usage:      required

  Value type: <string>

  Definition: "qcom,qbt-handler".

- qcom,ipc-gpio

  Usage:      required

  Value type: <phandle>

  Definition: phandle for GPIO to be used for IPC.

- qcom,finger-detect-gpio

  Usage:      required

  Value type: <phandle>

  Definition: phandle for GPIO to be used for finger detect.

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Example

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qcom,qbt_handler {

                compatible = "qcom,qbt-handler";

                qcom,ipc-gpio = <&tlmm 38 0>;

                qcom,finger-detect-gpio = <&tlmm 39 0>;

};