dt-bindings: input: Convert da906{1,2,3} onkey to json-schema

Convert the da906{1,2,3} onkey device tree binding documentation to
json-schema.

Update MAINTAINERS entries, description and onkey property by
referring to dlg,da9062-onkey binding file.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Link: https://lore.kernel.org/r/20240131102656.3379-4-biju.das.jz@bp.renesas.com


Signed-off-by: Lee Jones <lee@kernel.org>