dt-bindings: input: touchscreen: add compatible string for Goodix GT917S

Goodix GT917S is a new touchscreen chip from Goodix.

Add its compatible string to the device tree binding.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Bastien Nocera <hadess@hadess.net>
Link: https://lore.kernel.org/r/20200228010146.12215-2-icenowy@aosc.io


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>