dt-bindings: Add vendor prefix for Videostrong

Videostrong Technology Co., Ltd., A manufacturer of Android Players & STB
(Android with DVB Hybrid box & DVB-T2/S2/C/ISDB-T/DTMB-TH/ATSC) as well as
HD media players.

Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Mohammad Rasim <mohammad.rasim96@gmail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>