lib: add linear range index macro

Add linear_range_idx macro for declaring the linear_range struct simply.
Reviewed-by: Matti Vaittinen <mazziesaccount@gmail.com>
Signed-off-by: ChiaEn Wu <chiaen_wu@richtek.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

include/linux/linear_range.h

@@ -26,6 +26,17 @@ struct linear_range {
 	unsigned int step;
 };
 
+#define LINEAR_RANGE(_min, _min_sel, _max_sel, _step)		\
+	{							\
+		.min = _min,					\
+		.min_sel = _min_sel,				\
+		.max_sel = _max_sel,				\
+		.step = _step,					\
+	}
+
+#define LINEAR_RANGE_IDX(_idx, _min, _min_sel, _max_sel, _step)	\
+	[_idx] = LINEAR_RANGE(_min, _min_sel, _max_sel, _step)
+
 unsigned int linear_range_values_in_range(const struct linear_range *r);
 unsigned int linear_range_values_in_range_array(const struct linear_range *r,
 						int ranges);