devicetree: bindings: Add vendor prefix for Tronsmart

Tronsmart is a China based company building consumer electronic
devices.

Signed-off-by: Matthias Brugger <mbrugger@suse.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Carlo Caione <carlo@endlessm.com>