dt-bindings: input: touchscreen: st1232: add touch-overlay example

dt-bindings: input: touchscreen: st1232: add touch-overlay example

The touch-overlay feature adds support for segments (touch areas) on the
touchscreen surface that represent overlays with clipped touchscreen
areas and printed buttons.

Add nodes for a clipped touchscreen and overlay buttons to the existing
example.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Javier Carrasco <javier.carrasco@wolfvision.net>
Link: https://lore.kernel.org/r/20241016-feature-ts_virtobj_patch-v11-3-b292a1bbb0a1@wolfvision.net
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>