iio: pressure-core: st: Provide support for the Vdd power supply

The power to some of the sensors are controlled by regulators. In most
cases these are 'always on', but if not they will fail to work until
the regulator is enabled using the relevant APIs. This patch allows for
the Vdd power supply to be specified by either platform data or Device
Tree.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/include/linux/iio/common/st_sensors.h b/include/linux/iio/common/st_sensors.h
index e732fda..968b84e 100644
--- a/include/linux/iio/common/st_sensors.h
+++ b/include/linux/iio/common/st_sensors.h
@@ -16,6 +16,7 @@
 #include <linux/irqreturn.h>
 #include <linux/iio/trigger.h>
 #include <linux/bitops.h>
+#include <linux/regulator/consumer.h>
 
 #include <linux/platform_data/st_sensors_pdata.h>
 
@@ -201,6 +202,7 @@
  * @trig: The trigger in use by the core driver.
  * @sensor: Pointer to the current sensor struct in use.
  * @current_fullscale: Maximum range of measure by the sensor.
+ * @vdd: Pointer to sensor's Vdd power supply
  * @enabled: Status of the sensor (false->off, true->on).
  * @multiread_bit: Use or not particular bit for [I2C/SPI] multiread.
  * @buffer_data: Data used by buffer part.
@@ -216,6 +218,7 @@
 	struct iio_trigger *trig;
 	struct st_sensors *sensor;
 	struct st_sensor_fullscale_avl *current_fullscale;
+	struct regulator *vdd;
 
 	bool enabled;
 	bool multiread_bit;