pinctrl: Kconfig: Fix STMFX GPIO expander Pinctrl/GPIO driver dependencies

module_i2c_driver and pinconf_generic_dt_node_to_map_pin are undeclared
if CONFIG_I2C and CONFIG_OF are not enabled.

Fixes: 1490d9f8 ("pinctrl: Add STMFX GPIO expander Pinctrl/GPIO driver")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>