dt-bindings: Add vendor prefix for Satoz

Satoz is a Chinese TFT manufacturer.
Website: http://www.sat-sz.com/English/index.html

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200106151827.31511-1-miquel.raynal@bootlin.com