pinctrl: equilibrium: Convert to use struct pingroup

The pin control header provides struct pingroup.
Utilize it instead of open coded variants in the driver.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20231204160033.1872569-4-andriy.shevchenko@linux.intel.com


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