dt-bindings: Add vendor prefix for Acer Inc.

Acer is a hardware and electronics corporation, specializing in advanced
electronics technology. Acer's products include desktop PCs, laptop PCs,
tablets, servers, displays, storage devices, virtual reality devices,
smartphones and peripherals. Their web site is http://www.acer.com/

.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>