dt-bindings: iio: adc: ti-ads1298: Add bindings

Bindings for the TI ADS1298 medical ADC. This device is
typically used for ECG and similar measurements. Supports data
acquisition at configurable scale and sampling frequency.

The device has so many options for connecting stuff, at this
point the bindings aren't nearly complete but partial bindings
are better than no bindings at all.
Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240216153020.485201-1-mike.looijmans@topic.nlSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/ti,ads1298.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Texas Instruments' ads1298 medical ADC chips
+
+description: |
+  Datasheet at: https://www.ti.com/product/ADS1298
+  Bindings for this chip aren't complete.
+
+maintainers:
+  - Mike Looijmans <mike.looijmans@topic.nl>
+
+properties:
+  compatible:
+    enum:
+      - ti,ads1298
+
+  reg:
+    maxItems: 1
+
+  spi-cpha: true
+
+  reset-gpios:
+    maxItems: 1
+
+  avdd-supply:
+    description:
+      Analog power supply, voltage between AVDD and AVSS. When providing a
+      symmetric +/- 2.5V, the regulator should report 5V.
+
+  vref-supply:
+    description:
+      Optional reference voltage. If omitted, internal reference is used,
+      which is 2.4V when analog supply is below 4.4V, 4V otherwise.
+
+  clocks:
+    description: Optional 2.048 MHz external source clock on CLK pin
+    maxItems: 1
+
+  interrupts:
+    description: Interrupt on DRDY pin, triggers on falling edge
+    maxItems: 1
+
+  label: true
+
+required:
+  - compatible
+  - reg
+  - avdd-supply
+  - interrupts
+
+allOf:
+  - $ref: /schemas/spi/spi-peripheral-props.yaml#
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    #include <dt-bindings/interrupt-controller/irq.h>
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        adc@1 {
+          reg = <1>;
+          compatible = "ti,ads1298";
+          label = "ads1298-1-ecg";
+          avdd-supply = <&reg_iso_5v_a>;
+          clocks = <&clk_ads1298>;
+          interrupt-parent = <&gpio0>;
+          interrupts = <78 IRQ_TYPE_EDGE_FALLING>;
+          spi-max-frequency = <20000000>;
+          spi-cpha;
+        };
+    };
+...