iio: Add Freescale MPL3115A2 pressure / temperature sensor driver

I2C-controlled MEMS sensor with 20-bit pressure measurement (pascal) and
12-bit temperature measurement

driver only exposes basic functionality, see TODO remarks
datasheet: http://cache.freescale.com/files/sensors/doc/data_sheet/MPL3115A2.pdf

v2:
* store 20-bit value in 32-bit buffer element (instead of 24-bit)
* zero buffer to prevent kernel data leak to userspace
* fix mutex unlock in trigger handler (thanks Andi Shyti)

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
Reviewed-by: Andi Shyti <andi@etezian.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/drivers/iio/pressure/Kconfig b/drivers/iio/pressure/Kconfig
index 4f2e0f9..a8b9cae 100644
--- a/drivers/iio/pressure/Kconfig
+++ b/drivers/iio/pressure/Kconfig
@@ -5,6 +5,18 @@
 
 menu "Pressure sensors"
 
+config MPL3115
+	tristate "Freescale MPL3115A2 pressure sensor driver"
+	depends on I2C
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
+	help
+	  Say yes here to build support for the Freescale MPL3115A2
+	  pressure sensor / altimeter.
+
+          To compile this driver as a module, choose M here: the module
+          will be called mpl3115.
+
 config IIO_ST_PRESS
 	tristate "STMicroelectronics pressure sensor Driver"
 	depends on (I2C || SPI_MASTER) && SYSFS