dt-bindings: vendor-prefixes: Add Shanghai Top Display Optolelectronics vendor prefix

Shanghai Top Display Optolelectronics Co., Ltd  is a display manufacturer
from Shanghai.
Web site of the company: http://www.shtdo.com/



Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200915121912.4347-2-narmstrong@baylibre.com