mfd: lpc_ich: Expose the GPIO controller cell's software node

mfd: lpc_ich: Expose the GPIO controller cell's software node

One of the users of this driver - meraki-mx100 - abuses the software
node API by setting up a dummy software node without any logical link to
this GPIO controller and uses the fact that the GPIO core matches the
controller's label against the swnode's name to make the lookup work.

We want to remove this behavior from GPIOLIB in favor of actual matching
of firmware nodes but that would break this user. To facilitate that:
create a software node for the GPIO controller cell and expose its
address in the provided MFD header.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20260218-meraki-swnodes-v2-1-92c521da241c@oss.qualcomm.com
Signed-off-by: Lee Jones <lee@kernel.org>