dts: Deprecate ALTR as a vendor prefix

Because most of the vendor prefixes are lower case, deprecate
the vendor prefix "ALTR" in place of "altr" for Altera Corp..

Signed-off-by: Dinh Nguyen <dinguyen@altera.com>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: devicetree@vger.kernel.org
Signed-off-by: Olof Johansson <olof@lixom.net>