refactor: Move away from deprecated label usages.

* Move away from DT_LABEL.
* Move to DEVICE_DT_GET for non-behavior device access.
* Move various drivers to `gpio_spec_dt` and `DT` related macros.
* Remove mcp23017 while at it, since better upstream driver is
  available.

app/drivers/zephyr/dts/bindings/gpio/microchip,mcp23017.yaml

@@ -1,29 +0,0 @@
-#
-# Copyright (c) 2020 Geanix ApS
-#
-# SPDX-License-Identifier: Apache-2.0
-#
-
-description: >
-    This is a representation of the Microchip MCP23017 I2C Gpio Expander.
-
-compatible: "microchip,mcp23017"
-
-include: [gpio-controller.yaml, i2c-device.yaml]
-
-properties:
-    label:
-      required: true
-
-    "#gpio-cells":
-      const: 2
-
-    ngpios:
-      type: int
-      required: true
-      const: 16
-      description: Number of gpios supported
-
-gpio-cells:
-  - pin
-  - flags

app/drivers/zephyr/dts/bindings/gpio/zmk,gpio-595.yaml

@@ -12,9 +12,6 @@ compatible: "zmk,gpio-595"
 include: [gpio-controller.yaml, spi-device.yaml]
 
 properties:
-  label:
-    required: true
-
   "#gpio-cells":
     const: 2