[chassis][voq] Remove the leaf ref for the ifname in sonic-system-port.yang (#18855)

Microsoft ADO 27934751:

Fixes #18854

Update the sonic-system-port.yang to remove the check to have ifname as leafref in the port table
The system-port config table will have all the ports in the chassis not only to one linecard, so in case of the chassis with different linecards sku with different number of ports this leafref will not work.

Author: arlakshm

src/sonic-yang-models/yang-models/sonic-system-port.yang

@@ -40,13 +40,8 @@ module sonic-system-port {
                 }
 
                 leaf ifname {
-                    type union {
-                        type leafref {
-                            path /port:sonic-port/port:PORT/port:PORT_LIST/port:name;
-                        }
-                        type string {
-                            pattern "Cpu0";
-                        }
+                    type string {
+                        length 1..128;
                     }
                 }