checks: relax graph checks for overlays

[mriesch-wv]

In device tree overlays, the following patterns occur frequently:

board.dts:
/dts-v1/;

/ {
	display-controller {
		ports {
			#address-cells = <1>;
			#size-cells = <0>;

			vp0: port@0 {
				reg = <0>;

				vp0_out: endpoint {
				};
			};

			vp1: port@1 {
				reg = <1>;
			};
		};
	};
};

overlay-endpoint.dtso:
/dts-v1/;
/plugin/;

&{/} {
	hdmi-tx-connector {
		port {
			hdmi_tx_in: endpoint {
				remote-endpoint = <&vp0_out>;
			};
		};
	};
};

&vp0_out {
	remote-endpoint = <&hdmi_tx_in>;
};

In this case, dtc expects that the node referenced by &vp0_out is named "endpoint", but the name cannot be inferred. Also, dtc complains about the connections between the endpoints not being bidirectional.

Similarly, for a different overlay overlay-port.dtso:

/dts-v1/;
/plugin/;

&{/} {
	panel {
		port {
			panel_in: endpoint {
				remote-endpoint = <&vp1_out>;
			};
		};
	};
};

&vp1 {
	vp1_out: endpoint {
		remote-endpoint = <&panel_in>;
	};
};

dtc expects that the node referenced by &vp1 is named "port", but the name cannot be inferred.

Relax the corresponding checks and skip the parts that are not reasonable for device tree overlays.

[dgibson]

Sorry it's taken me so long to get around to looking at this. TBH, I don't really understand what the graph checks are doing, so I'll just take your word for it.

Applied.

[mriesch-wv]

@dgibson Cool, thanks!