pinctrl: starfive: Convert to use grp member

pinctrl: starfive: 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.

Reviewed-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20231211190321.307330-13-andriy.shevchenko@linux.intel.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>