gpio: generic: add new generic GPIO chip API

gpio: generic: add new generic GPIO chip API

As the first step in removing the fields specific to the gpio-mmio
module from struct gpio_chip, we introduce a new set of generic GPIO
chip interfaces that are meant to replace the existing bgpio_ ones.

The new initialization function - gpio_generic_chip_init() - takes a
configuration structure as argument instead of 9 separate parameters.
This will allow easy extension if needed in the future. We hide the
locking details behind a set of helpers in order to be able to move the
raw spinlock out of struct gpio_chip without the users noticing.

For now, the new APIs just wrap the existing ones. Once all users have
been converted to the new interfaces, we'll pull them into gpio-mmio and
implement them in a backward-compatible way while also moving all fields
specific to the generic GPIO chip into struct gpio_generic_chip.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20250702-gpio-mmio-rework-v2-1-6b77aab684d8@linaro.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>