mfd: syscon: Return -ENOSYS if CONFIG_MFD_SYSCON is not enabled

Some platforms may not define CONFIG_MFD_SYSCON (or haven't syscon),
it can fix build error for these platforms.
Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

include/linux/mfd/syscon.h

@@ -17,10 +17,35 @@
 
 struct device_node;
 
+#ifdef CONFIG_MFD_SYSCON
 extern struct regmap *syscon_node_to_regmap(struct device_node *np);
 extern struct regmap *syscon_regmap_lookup_by_compatible(const char *s);
 extern struct regmap *syscon_regmap_lookup_by_pdevname(const char *s);
 extern struct regmap *syscon_regmap_lookup_by_phandle(
 					struct device_node *np,
 					const char *property);
+#else
+static inline struct regmap *syscon_node_to_regmap(struct device_node *np)
+{
+	return ERR_PTR(-ENOSYS);
+}
+
+static inline struct regmap *syscon_regmap_lookup_by_compatible(const char *s)
+{
+	return ERR_PTR(-ENOSYS);
+}
+
+static inline struct regmap *syscon_regmap_lookup_by_pdevname(const char *s)
+{
+	return ERR_PTR(-ENOSYS);
+}
+
+static inline struct regmap *syscon_regmap_lookup_by_phandle(
+					struct device_node *np,
+					const char *property)
+{
+	return ERR_PTR(-ENOSYS);
+}
+#endif
+
 #endif /* __LINUX_MFD_SYSCON_H__ */