pinctrl: pxa2xx: 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 <andriy.shevchenko@linux.intel.com>
Message-ID: <20240311140833.1168742-1-andriy.shevchenko@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>