pinctrl: th1520: add a CONFIG_OF dependency

pinctrl: th1520: add a CONFIG_OF dependency

When compile-testing without CONfIG_OF:

drivers/pinctrl/pinctrl-th1520.c: In function 'th1520_pinctrl_dt_node_to_map':
drivers/pinctrl/pinctrl-th1520.c:455:23: error: implicit declaration of function 'pinconf_generic_parse_dt_config'; did you mean 'pinconf_generic_dump_config'? [-Wimplicit-function-declaration]
  455 |                 ret = pinconf_generic_parse_dt_config(child, pctldev, &configs, &nconfigs);
      |                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |                       pinconf_generic_dump_config

Enforce this using Kconig dependencies.

Fixes: bed5cd6f8a98 ("pinctrl: Add driver for the T-Head TH1520 SoC")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Drew Fustini <drew@pdp7.com>
Link: https://lore.kernel.org/20241015151126.2401855-1-arnd@kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>