It seems that there is problem with your dpl file, please modify LSDK 21.08 original DPL file dpl-eth.19.dts as the following.
/* ------------ DPNIs --------------*/
obj_set@dpni {
type = "dpni";
ids = <0x0 0x1>;
};
Modify to:
obj_set@dpni {
type = "dpni";
ids = <0x0 0x1 0x2 0x3>;
};
Then adding the following section in "Connections" section.
connection@3 {
endpoint1 = "dpni@2";
endpoint2 = "dpmac@3";
};
connection@4 {
endpoint1 = "dpni@3";
endpoint2 = "dpmac@4";
};