pinctrl: Modify Kconfig to fix linker error

Fix below linker error

    ld: drivers/pinctrl/pinctrl-equilibrium.o: in function
    `pinconf_generic_dt_node_to_map_all':
    pinctrl-equilibrium.c:(.text+0xb): undefined reference
    to `pinconf_generic_dt_node_to_map'

Caused by below commit

    1948d5c5 ("pinctrl: Add pinmux & GPIO controller driver for a new SoC")

by adding 'depends on OF' in Kconfig driver entry.
Reported-by: Randy Dunlap <rdunlap@infradead.org&gt;>
Signed-off-by: Rahul Tanwar <rahul.tanwar@linux.intel.com>
Link: https://lore.kernel.org/r/ba937f271d1a2173828a2325990d62cb36d61595.1575514110.git.rahul.tanwar@linux.intel.com
Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/Kconfig

@@ -422,6 +422,7 @@ config PINCTRL_TB10X
 
 config PINCTRL_EQUILIBRIUM
 	tristate "Generic pinctrl and GPIO driver for Intel Lightning Mountain SoC"
+	depends on OF
 	select PINMUX
 	select PINCONF
 	select GPIOLIB