pinctrl: sh-pfc: refactor voltage setting

All known hardware being able to switch voltages has the same POCCTRL
register. So, factor out the common code to the core and keep only
the pin-to-bit mapping SoC specific. Convert the only user, r8a7790.
In case POCCTRL should ever get more complex (more voltages to select?),
we should probably switch over to a describing array like drive strength
does currently.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
diff --git a/drivers/pinctrl/sh-pfc/sh_pfc.h b/drivers/pinctrl/sh-pfc/sh_pfc.h
index 656ea32..ea3a527 100644
--- a/drivers/pinctrl/sh-pfc/sh_pfc.h
+++ b/drivers/pinctrl/sh-pfc/sh_pfc.h
@@ -189,9 +189,7 @@
 	unsigned int (*get_bias)(struct sh_pfc *pfc, unsigned int pin);
 	void (*set_bias)(struct sh_pfc *pfc, unsigned int pin,
 			 unsigned int bias);
-	int (*get_io_voltage)(struct sh_pfc *pfc, unsigned int pin);
-	int (*set_io_voltage)(struct sh_pfc *pfc, unsigned int pin,
-			      u16 voltage_mV);
+	int (*pin_to_pocctrl)(struct sh_pfc *pfc, unsigned int pin, u32 *pocctrl);
 };
 
 struct sh_pfc_soc_info {