pinctrl: generic: Fix compilation error

The function definition of pinconf_generic_dump_config is defined
under CONFIG_DEBUG_FS macro. Define the declaration too under this macro.

Without this patch we get the following build error:
drivers/built-in.o: In function `pcs_pinconf_config_dbg_show':
drivers/pinctrl/pinctrl-single.c:726: undefined reference to
`pinconf_generic_dump_config'
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/pinconf.h

@@ -90,7 +90,7 @@ static inline void pinconf_init_device_debugfs(struct dentry *devroot,
  * pin config.
  */
 
-#ifdef CONFIG_GENERIC_PINCONF
+#if defined(CONFIG_GENERIC_PINCONF) && defined(CONFIG_DEBUG_FS)
 
 void pinconf_generic_dump_pin(struct pinctrl_dev *pctldev,
 			      struct seq_file *s, unsigned pin);