pinctrl: equilibrium: Make use of struct pinfunction

Since pin control provides a generic data type for the pin function,
use it in the driver.

Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20240530085745.1539925-3-andy.shevchenko@gmail.com


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