dt-bindings: arm: realtek: Tidy up conversion to json-schema

Restore the device names for compatible strings as comments.
Prepare for adding more SoCs by inserting oneOf.

Fixes: 693af5f3 ("dt-bindings: arm: Convert Realtek board/soc bindings to json-schema")
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Andreas Färber <afaerber@suse.de>