DT: add Olimex to vendor prefixes

This company already provided some products, so add them to the
vendor prefix list.
Signed-off-by: NStefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: NRob Herring <robh@kernel.org>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -161,6 +161,7 @@ nuvoton	Nuvoton Technology Corporation
 nvidia	NVIDIA
 nxp	NXP Semiconductors
 okaya	Okaya Electric America, Inc.
+olimex	OLIMEX Ltd.
 onnn	ON Semiconductor Corp.
 opencores	OpenCores.org
 option	Option NV