pinctrl: provide pinmux_generic_add_pinfunction()

Several drivers call pinmux_generic_add_function() passing it the
contents of struct pinfunction as first three arguments. We can make
this shorter by simply providing an interface allowing to pass the
address of struct pinfunction directly when adding a new function.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Link: https://lore.kernel.org/20250709-pinctrl-gpio-pinfuncs-v2-2-b6135149c0d9@linaro.org


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>