* Keepalive Driver

Required properties:
- compatible : "sony,keepalive_cm4"

Optional properties:
- keepalive-interval: Duration of keepalive-interval (If not specified defaults to 50 s)
- response-wait-timer: response waiting timer value (If not specified defaults to 2 s)

Example:
	keepalive_cm4{
		compatible = "sony,keepalive_cm4";
		keepalive-interval = <50>;
		response-wait-timer = <2>;
		status = "okay";
	};

