pinctrl: zynq: add CONFIG_OF dependency

pinctrl: zynq: add CONFIG_OF dependency

The zynq driver can be enabled for compile-testing on builds without
CONFIG_OF, leading to a link error:

ld.lld-21: error: undefined symbol: pinconf_generic_dt_node_to_map
 referenced by pinconf-generic.h:231 (/home/arnd/arm-soc/include/linux/pinctrl/pinconf-generic.h:231)
          drivers/pinctrl/pinctrl-zynq.o:(pinconf_generic_dt_node_to_map_all) in archive vmlinux.a

Prevent this with the proper compile time dependency.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202506212021.deAhuaWr-lkp@intel.com/
Fixes: 1982621decaf ("pinctrl: Allow compile testing for K210, TB10X and ZYNQ")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/20250620130814.2580678-1-arnd@kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>