pinctrl: mediatek: Convert to use grp member

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

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20231211190321.307330-11-andriy.shevchenko@linux.intel.com


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