dt-bindings: Add vendor prefix for Motorola

Motorola was involved in semiconductor and mobile phone business.
The "motorola," prefix is already used by a couple of bindings:

* rtc/rtc-cmos.txt
* mfd/motorola-cpcap.txt
* regulator/cpcap-regulator.txt

Apart from that it is used in the DT file for the Droid 4 mobile
phone.
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -190,6 +190,7 @@ minix	MINIX Technology Ltd.
 miramems	MiraMEMS Sensing Technology Co., Ltd.
 mitsubishi	Mitsubishi Electric Corporation
 mosaixtech	Mosaix Technologies, Inc.
+motorola	Motorola, Inc.
 moxa	Moxa
 mpl	MPL AG
 mqmaker	mqmaker Inc.