gpiolib: Add stubs for gpiod lookup table interface

Add stubs for gpiod_add_lookup_table() and gpiod_remove_lookup_table()
for the !GPIOLIB case to prevent build errors.
Signed-off-by: Anatolij Gustschin <agust@denx.de>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

include/linux/gpio/machine.h

@@ -56,7 +56,14 @@ struct gpiod_lookup_table {
 	.flags = _flags,                                                  \
 }
 
+#ifdef CONFIG_GPIOLIB
 void gpiod_add_lookup_table(struct gpiod_lookup_table *table);
 void gpiod_remove_lookup_table(struct gpiod_lookup_table *table);
+#else
+static inline
+void gpiod_add_lookup_table(struct gpiod_lookup_table *table) {}
+static inline
+void gpiod_remove_lookup_table(struct gpiod_lookup_table *table) {}
+#endif
 
 #endif /* __LINUX_GPIO_MACHINE_H */