dt-bindings: touchscreen: Add touchscreen schema

Add touchscreen schema for common properties

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200108091118.5130-2-benjamin.gaignard@st.com


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