iio: add adjd_s311 I2C digital color sensor driver

sensor has 4 channels (10-bit each, R/G/B and clear), sensitivity
and gain is controlled in the driver by ext_info integration_time
and CHAN_INFO_HARDWAREGAIN

driver supports triggered buffer and IIO_CHAN_INFO_RAW to get the
sensor data

v5: address comments by Jonathan Cameron
* use macro for channel declaration
* get timestamp right before measurement
* cleanups

v4: address comments by Lars-Peter Clausen
* make sure trigger handler is exited with iio_trigger_notify_done()
  and IRQ_HANDLED
* kfree()/kalloc() -> krealloc()

v3:
* fix warnings

v2: address comments by Lars-Peter Clausen
* buffer allocation now in update_scan_mode instead of in trigger
  handler
* simplify trigger code (assume active_scan_mask is not empty, use
  for_each_set_bit, use iio_push_to_buffer)
* reorder entry in Makefile and Kconfig
* fix remove

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/drivers/iio/light/Kconfig b/drivers/iio/light/Kconfig
index f3ea90d..91d15d2 100644
--- a/drivers/iio/light/Kconfig
+++ b/drivers/iio/light/Kconfig
@@ -3,6 +3,18 @@
 #
 menu "Light sensors"
 
+config ADJD_S311
+	tristate "ADJD-S311-CR999 digital color sensor"
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
+	depends on I2C
+	help
+	 If you say yes here you get support for the Avago ADJD-S311-CR999
+	 digital color light sensor.
+
+	 This driver can also be built as a module.  If so, the module
+	 will be called adjd_s311.
+
 config SENSORS_LM3533
 	tristate "LM3533 ambient light sensor"
 	depends on MFD_LM3533