gpio: elkhartlake: Convert to auxiliary driver

gpio: elkhartlake: Convert to auxiliary driver

Since PCI device should not be abusing platform device, MFD parent to
platform child path is no longer being pursued for this driver. Convert
it to auxiliary driver, which will be used by EHL PSE auxiliary device.

Signed-off-by: Raag Jadav <raag.jadav@intel.com>
Acked-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20251112034040.457801-3-raag.jadav@intel.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>