* 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.
The key scanning drivers are now automatically enabled when a DT node
with the matching "compatible" property is present and enabled, so they
no longer need to be manually set for each board.