pinctrl: Introduce struct pinfunction and PINCTRL_PINFUNCTION() macro

There are many pin control drivers define their own data type for
pin function representation which is the same or embed the same data
as newly introduced one. Provide the data type and convenient macro
for all pin control drivers.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>

include/linux/pinctrl/pinctrl.h

@@ -206,6 +206,26 @@ extern int pinctrl_get_group_pins(struct pinctrl_dev *pctldev,
 				const char *pin_group, const unsigned **pins,
 				unsigned *num_pins);
 
+/**
+ * struct pinfunction - Description about a function
+ * @name: Name of the function
+ * @groups: An array of groups for this function
+ * @ngroups: Number of groups in @groups
+ */
+struct pinfunction {
+	const char *name;
+	const char * const *groups;
+	size_t ngroups;
+};
+
+/* Convenience macro to define a single named pinfunction */
+#define PINCTRL_PINFUNCTION(_name, _groups, _ngroups)	\
+(struct pinfunction) {					\
+		.name = (_name),			\
+		.groups = (_groups),			\
+		.ngroups = (_ngroups),			\
+	}
+
 #if IS_ENABLED(CONFIG_OF) && IS_ENABLED(CONFIG_PINCTRL)
 extern struct pinctrl_dev *of_pinctrl_get(struct device_node *np);
 #else