wifi: ath9k: Obtain system GPIOS from descriptors

wifi: ath9k: Obtain system GPIOS from descriptors

The ath9k has an odd use of system-wide GPIOs: if the chip
does not have internal GPIO capability, it will try to obtain a
GPIO line from the system GPIO controller:

  if (BIT(gpio) & ah->caps.gpio_mask)
        ath9k_hw_gpio_cfg_wmac(...);
  else if (AR_SREV_SOC(ah))
        ath9k_hw_gpio_cfg_soc(ah, gpio, out, label);

Where ath9k_hw_gpio_cfg_soc() will attempt to issue
gpio_request_one() passing the local GPIO number of the controller
(0..31) to gpio_request_one().

This is somewhat peculiar and possibly even dangerous: there is
nowadays no guarantee of the numbering of these system-wide
GPIOs, and assuming that GPIO 0..31 as used by ath9k would
correspond to GPIOs 0..31 on the system as a whole seems a bit
wild.

Register all 32 GPIOs at index 0..31 directly in the ATH79K
GPIO driver and associate with the NULL device (making them
widely available) if and only if we are probing ATH79K wifi
from the AHB bus (used for SoCs). We obtain these offsets from
the NULL device if necessary.

These GPIOs should ideally be defined in the device tree
instead, but we have no control over that for the legacy
code path.

Testcompiled with the ath79 defconfig.

Reported-by: Michał Kępień <kernel@kempniu.pl>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Signed-off-by: Linus Walleij <linusw@kernel.org>
Tested-by: Michał Kępień <kernel@kempniu.pl>
Link: https://patch.msgid.link/20260317-descriptors-wireless-v6-1-b19ecff9cd2b@kernel.org
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>