iio: hid: Add humidity sensor support

Environmental humidity sensor is a hid defined sensor,
it shows raw humidity measurement of air.

More information can be found in:
http://www.usb.org/developers/hidpage/HUTRR39b.pdf

According to IIO ABI definition, humidityrelative data output unit is
milli percent. Add the unit convert from percent to milli percent.

Signed-off-by: Song Hongyan <hongyan.song@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/drivers/iio/humidity/Kconfig b/drivers/iio/humidity/Kconfig
index 912477d..14b9ce4 100644
--- a/drivers/iio/humidity/Kconfig
+++ b/drivers/iio/humidity/Kconfig
@@ -36,6 +36,20 @@
 	  To compile this driver as a module, choose M here: the module
 	  will be called hdc100x.
 
+config HID_SENSOR_HUMIDITY
+	tristate "HID Environmental humidity sensor"
+	depends on HID_SENSOR_HUB
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
+	select HID_SENSOR_IIO_COMMON
+	select HID_SENSOR_IIO_TRIGGER
+	help
+	  Say yes here to build support for the HID SENSOR
+	  humidity driver
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called hid-sensor-humidity.
+
 config HTS221
 	tristate "STMicroelectronics HTS221 sensor Driver"
 	depends on (I2C || SPI)