dt-bindings: panel: Convert raydium,rm68200 to json-schema

Convert raydium,rm68200 to json-schema.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Philippe Cornu <philippe.cornu@st.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200206133344.724-3-benjamin.gaignard@st.com