dts: bindings: move adc devicetree binding to top level

Move the devicetree bindings for Analog-to-Digital Converters (ADCs)
from dts/bindings/iio/adc to dts/bindings/adc as Zephyr does not have
an IIO layer.

Signed-off-by: Benjamin Björnsson <benjamin.bjornsson@gmail.com>

dts/bindings/adc/nuvoton,npcx-adc.yaml

@@ -0,0 +1,33 @@
+# Copyright (c) 2020 Nuvoton Technology Corporation.
+# SPDX-License-Identifier: Apache-2.0
+
+description: Nuvoton, NPCX-ADC node
+
+compatible: "nuvoton,npcx-adc"
+
+include: [adc-controller.yaml, pinctrl-device.yaml]
+
+properties:
+  reg:
+    required: true
+  clocks:
+    required: true
+  pinctrl-0:
+    required: true
+  pinctrl-names:
+    required: true
+  channel-count:
+    type: int
+    required: true
+    description: the number of ADC channels
+  threshold-reg-offset:
+    type: int
+    required: true
+    description: the offset of threshold detector register address
+  threshold-count:
+    type: int
+    required: true
+    description: the number of threshold detectors adc supports
+
+io-channel-cells:
+  - input

dts/bindings/adc/nxp,lpc-lpadc.yaml

@@ -0,0 +1,56 @@
+# Copyright (c) 2020, Toby Firth
+# SPDX-License-Identifier: Apache-2.0
+
+description: LPC LPADC
+
+compatible: "nxp,lpc-lpadc"
+
+include: [adc-controller.yaml, pinctrl-device.yaml]
+
+properties:
+  reg:
+    required: true
+
+  interrupts:
+    required: true
+
+  clk-divider:
+    type: int
+    required: true
+    description: clock divider for the converter
+
+  clk-source:
+    type: int
+    required: true
+    description: source to attach the ADC clock to
+
+  voltage-ref:
+    type: int
+    required: true
+    description: reference voltage source
+
+  calibration-average:
+    type: int
+    required: true
+    description: conversion average number for auto-calibration
+
+  power-level:
+    type: int
+    required: true
+    description: power level for the ADC
+
+  offset-value-a:
+    type: int
+    required: true
+    description: Offset value A to use if CONFIG_LPADC_DO_OFFSET_CALIBRATION is false
+
+  offset-value-b:
+    type: int
+    required: true
+    description: Offset value B to use if CONFIG_LPADC_DO_OFFSET_CALIBRATION is false
+
+  "#io-channel-cells":
+    const: 1
+
+io-channel-cells:
+  - input