ARM: bcm2835: dt: Add vendor prefix for Raspberry Pi

Since the prefix is already in use, we need to add it in the
vendor list.
Reviewed-by: NStephen Warren <swarren@wwwdotorg.org>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NStefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: NLee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -159,6 +159,7 @@ radxa	Radxa
 raidsonic	RaidSonic Technology GmbH
 ralink	Mediatek/Ralink Technology Corp.
 ramtron	Ramtron International
+raspberrypi	Raspberry Pi Foundation
 realtek Realtek Semiconductor Corp.
 renesas	Renesas Electronics Corporation
 ricoh	Ricoh Co. Ltd.