[U-Boot] [PATCH] pinctrl: renesas: Fix linker error when PINCTRL_PFC=n

[Eugeniu Rosca]

With CONFIG_PINCTRL_PFC=n, aarch64-linux-gnu-ld reports:

-----8<-----
  LD      u-boot
drivers/gpio/built-in.o: In function `rcar_gpio_request':
drivers/gpio/gpio-rcar.c:128: undefined reference to `sh_pfc_config_mux_for_gpio'
-----8<-----

Fix it in the least intrusive way and *avoid* ifdefs in the *.c code.

Some recent Linux commits sharing the same approach:
 - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=23222f8f8dce
   ("acpi, nfit: Add function to look up nvdimm device and provide SMBIOS handle")
 - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5f143af7501e
   ("spi: make OF helper available for others")
 - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=bccd06223f21
   ("IB/uverbs: Add UVERBS_ATTR_FLAGS_IN to the specs language")

Fixes: f6e545a73f88 ("pfc: rmobile: Add hook to configure pin as GPIO")
Reported-by: Dirk Behme <dirk.behme at de.bosch.com>
Signed-off-by: Eugeniu Rosca <erosca at de.adit-jv.com>
---
 drivers/pinctrl/renesas/sh_pfc.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/pinctrl/renesas/sh_pfc.h b/drivers/pinctrl/renesas/sh_pfc.h
index b98c2f185d26..3d95d3c725cf 100644
--- a/drivers/pinctrl/renesas/sh_pfc.h
+++ b/drivers/pinctrl/renesas/sh_pfc.h
@@ -261,7 +261,15 @@ void sh_pfc_write(struct sh_pfc *pfc, u32 reg, u32 data);
 const struct pinmux_bias_reg *
 sh_pfc_pin_to_bias_reg(const struct sh_pfc *pfc, unsigned int pin,
 		       unsigned int *bit);
+#if IS_ENABLED(CONFIG_PINCTRL_PFC)
 int sh_pfc_config_mux_for_gpio(struct udevice *dev, unsigned pin_selector);
+#else
+static inline
+int sh_pfc_config_mux_for_gpio(struct udevice *dev, unsigned pin_selector)
+{
+	return -ENODEV;
+}
+#endif
 
 extern const struct sh_pfc_soc_info r8a7790_pinmux_info;
 extern const struct sh_pfc_soc_info r8a7791_pinmux_info;
-- 
2.21.0