platform/x86: pcengines-apuv2: attach software node to the gpiochip

platform/x86: pcengines-apuv2: attach software node to the gpiochip

GPIO subsystem is switching the way it locates GPIO chip instances for
GPIO references in software nodes from matching on node names to
identity matching, which necessitates assigning firmware nodes
(software nodes) to GPIO chips.

Attach apu2_gpiochip_node to the platform device representing the GPIO
controller.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Link: https://patch.msgid.link/aY-oAVI0TubcaD2K@google.com
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>