dt-bindings: Add 1027/1029/1031 SPI ADCs as trivial devices

In the same time, remove the dedicated bindings file which is now
useless.

Signed-off-by: Miquel Raynal <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

Documentation/devicetree/bindings/iio/adc/max1027-adc.txt

···
-* Maxim 1027/1029/1031 Analog to Digital Converter (ADC)
-
-Required properties:
-  - compatible: Should be "maxim,max1027" or "maxim,max1029" or "maxim,max1031"
-  - reg: SPI chip select number for the device
-
-Optional properties:
-  - interrupts: IRQ line for the ADC
-  see: Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
-
-Recommended properties:
-- spi-max-frequency: Definition as per
-                     Documentation/devicetree/bindings/spi/spi-bus.txt
-
-Example:
-adc@0 {
-	compatible = "maxim,max1027";
-	reg = <0>;
-	interrupt-parent = <&gpio5>;
-	interrupts = <15 IRQ_TYPE_EDGE_RISING>;
-	spi-max-frequency = <1000000>;
-};

Documentation/devicetree/bindings/trivial-devices.yaml

···
           - isil,isl68137
             # 5 Bit Programmable, Pulse-Width Modulator
           - maxim,ds1050
+            # 10-bit 8 channels 300ks/s SPI ADC with temperature sensor
+          - maxim,max1027
+            # 10-bit 12 channels 300ks/s SPI ADC with temperature sensor
+          - maxim,max1029
+            # 10-bit 16 channels 300ks/s SPI ADC with temperature sensor
+          - maxim,max1031
             # Low-Power, 4-/12-Channel, 2-Wire Serial, 12-Bit ADCs
           - maxim,max1237
             # PECI-to-I2C translator for PECI-to-SMBus/I2C protocol conversion