pinctrl: Export pinctrl_get_group_selector()

pinctrl: Export pinctrl_get_group_selector()

The recently added UltraRISC DP1000 is using this symbol, and in
a reasonable way as well, so export it.

Acked-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: Link: https://lore.kernel.org/linux-gpio/20260613164847.GA3152104@ax162/
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202606130210.ytVPxHlm-lkp@intel.com/
Fixes: cb7037924836 ("pinctrl: ultrarisc: Add UltraRISC DP1000 pinctrl driver")
Signed-off-by: Linus Walleij <linusw@kernel.org>