iio: Add Lite-On ltr501 ambient light / proximity sensor driver

combined ambient light (two channels) and proximity sensor with I2C
interface; the ALS channels are visible+IR and IR

datasheet is here
http://optoelectronics.liteon.com/upload/download/DS86-2012-0006/P_100_LTR-501ALS-01_PrelimDS_ver1.1.pdf

v3:
* fix use of sizeof in _read_als()
v2: (thanks to Lars-Peter Clausen)
* cannot use devm_iio_device_register() due to cleanup order in _remove()
* mutex around data wait/read
* turn info message in _probe() into check for part number
* change copyright year to 2014

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Author: pmeerw

drivers/iio/light/Kconfig

@@ -90,6 +90,18 @@ config SENSORS_LM3533
 	  changes. The ALS-control output values can be set per zone for the
 	  three current output channels.
 
+config LTR501
+	tristate "LTR-501ALS-01 light sensor"
+	depends on I2C
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
+	help
+	 If you say yes here you get support for the Lite-On LTR-501ALS-01
+	 ambient light and proximity sensor.
+
+	 This driver can also be built as a module.  If so, the module
+         will be called ltr501.
+
 config TCS3472
 	tristate "TAOS TCS3472 color light-to-digital converter"
 	depends on I2C

drivers/iio/light/Makefile

@@ -10,6 +10,7 @@ obj-$(CONFIG_CM36651)		+= cm36651.o
 obj-$(CONFIG_GP2AP020A00F)	+= gp2ap020a00f.o
 obj-$(CONFIG_HID_SENSOR_ALS)	+= hid-sensor-als.o
 obj-$(CONFIG_SENSORS_LM3533)	+= lm3533-als.o
+obj-$(CONFIG_LTR501)		+= ltr501.o
 obj-$(CONFIG_SENSORS_TSL2563)	+= tsl2563.o
 obj-$(CONFIG_TCS3472)		+= tcs3472.o
 obj-$(CONFIG_TSL4531)		+= tsl4531.o