pinctrl: keembay: Convert to use func member

Convert drivers to use func member embedded in struct function_desc,
because other members will be removed to avoid duplication and
desynchronisation of the generic pin function description.

Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20240530085745.1539925-10-andy.shevchenko@gmail.com


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