feat: Add nrf VDDH battery driver

Added a driver which uses the nRF52's ADC channel on the VDDH pin to
read the battery voltage when using high voltage mode.

app/drivers/zephyr/dts/bindings/sensor/zmk,battery-nrf-vddh.yaml

@@ -0,0 +1,11 @@
+# Copyright (c) 2021 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+description: Battery SoC monitoring using nRF VDDH
+
+compatible: "zmk,battery-nrf-vddh"
+
+properties:
+  label:
+    required: true
+    type: string