pinctrl: add stubs for OF-specific pinconf functions

Allow building drivers using these interfaces with COMPILE_TEST enabled
and OF disabled by providing stub definitions.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202505072245.OgSXI1hh-lkp@intel.com/


Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Link: https://lore.kernel.org/20250507143551.47056-1-brgl@bgdev.pl


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