devicetree: Add documentation for UPISEMI us5182d ALS and Proximity sensor

Added entries in i2c/vendor-prefixes for the us5182d als and proximity sensor.
Also added a documentation file for this sensor's properties.
Signed-off-by: Adriana Reus <adriana.reus@intel.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/light/us5182d.txt

+* UPISEMI us5182d I2C ALS and Proximity sensor
+
+Required properties:
+- compatible: must be "upisemi,usd5182"
+- reg: the I2C address of the device
+
+Optional properties:
+- upisemi,glass-coef: glass attenuation factor - compensation factor of
+                      resolution 1000 for material transmittance.
+- upisemi,dark-ths: array of 8 elements containing 16-bit thresholds (adc
+                    counts) corresponding to every scale.
+- upisemi,upper-dark-gain: 8-bit dark gain compensation factor(4 int and 4
+                           fractional bits - Q4.4) applied when light > threshold
+- upisemi,lower-dark-gain: 8-bit dark gain compensation factor(4 int and 4
+                           fractional bits - Q4.4) applied when light < threshold
+
+If the optional properties are not specified these factors will default to the
+values in the below example.
+The glass-coef defaults to no compensation for the covering material.
+The threshold array defaults to experimental values that work with US5182D
+sensor on evaluation board - roughly between 12-32 lux.
+There will be no dark-gain compensation by default when ALS > thresh
+(0 * dark-gain), and a 1.35 compensation factor when ALS < thresh.
+
+Example:
+
+    usd5182@39 {
+                compatible = "upisemi,usd5182";
+                reg = <0x39>;
+                upisemi,glass-coef = < 1000 >;
+                upisemi,dark-ths = /bits/ 16 <170 200 512 512 800 2000 4000 8000>;
+                upisemi,upper-dark-gain = /bits/ 8 <0x00>;
+                upisemi,lower-dark-gain = /bits/ 8 <0x16>;
+    };

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -214,6 +214,7 @@ toshiba	Toshiba Corporation
 toumaz	Toumaz
 tplink	TP-LINK Technologies Co., Ltd.
 truly	Truly Semiconductors Limited
+upisemi	uPI Semiconductor Corp.
 usi	Universal Scientific Industrial Co., Ltd.
 v3	V3 Semiconductor
 variscite	Variscite Ltd.