iio: Add macro to populate struct iio_map array

The GPIO core provides a handy GPIO_LOOKUP() macro to populate a struct
gpiod_lookup array without having to spell out attribute names (but
still avoid breakage when attributes within the struct are rearranged
or added).

The axp288_adc.c driver uses a similar macro to populate a struct
iio_map array.  Make it available to others.

Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
diff --git a/include/linux/iio/machine.h b/include/linux/iio/machine.h
index 1601a2a..5e1cfa7 100644
--- a/include/linux/iio/machine.h
+++ b/include/linux/iio/machine.h
@@ -28,4 +28,11 @@ struct iio_map {
 	void *consumer_data;
 };
 
+#define IIO_MAP(_provider_channel, _consumer_dev_name, _consumer_channel) \
+{									  \
+	.adc_channel_label = _provider_channel,				  \
+	.consumer_dev_name = _consumer_dev_name,			  \
+	.consumer_channel  = _consumer_channel,				  \
+}
+
 #endif