dt-bindings: Add vendor prefix for Hwacom Systems Inc.

Hwacom Systems Inc. is a broadband system integrator and supplier of
mobile, fixed and IP networks related services as well as
multimedia application. Website: http://www.hwacom.com/

Signed-off-by: Carlo Caione <carlo@endlessm.com>
Acked-by: Rob Herring <robh@kernel.org>
[khilman: change shortlog prefix to dt-bindings]
Signed-off-by: Kevin Hilman <khilman@baylibre.com>