dt-bindings: Add vendor prefix for Amarula Solutions

Added 'amarula' as a vendor prefix for Amarula Solutions,
specialist in Embedded and Opensource solutions.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>