arm64: dts: rockchip: add px30 otp controller

The px30 soc contains a controller for one-time-programmable memory,
so add the necessary node for it and the fields defined in it by default.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20191023224113.3268-1-heiko@sntech.de