drivers: adc: add ADC driver for EFM32

This adds a driver for ADCs available on EFM32

Signed-off-by: Wojciech Sipak <wsipak@antmicro.com>

dts/bindings/adc/silabs,gecko-adc.yaml

@@ -0,0 +1,25 @@
+# Copyright (c) 2023 Antmicro <www.antmicro.com>
+# SPDX-License-Identifier: Apache-2.0
+
+description: Silicon Labs Gecko Series 1 ADC
+
+compatible: "silabs,gecko-adc"
+
+include: adc-controller.yaml
+
+properties:
+  reg:
+    required: true
+
+  interrupts:
+    required: true
+
+  frequency:
+    type: int
+    required: true
+
+  "#io-channel-cells":
+    const: 1
+
+io-channel-cells:
+  - input