add address-cells = <0> to suppress warnings

The DTC of version 1.6.1 generates the warning "Missing #address-cells
in interrupt provider". add `address-cells = <0>` to suppress "Missing
\#address-cells" warning provided by DTC v1.6.1

Reference: [sysprog21#37](sysprog21#37)

scripts/gen-hart-dts.py

@@ -68,6 +68,7 @@ def dtsi_template (cpu_list: str, plic_list, sswi_list, mtimer_list, mswi_list,
 
         sswi0: sswi@4500000 {{
           #interrupt-cells = <0>;
+          #address-cells = <0>;
           interrupt-controller;
           interrupts-extended = {sswi_list};
           reg = <0x4500000 0x4000>;
@@ -76,6 +77,7 @@ def dtsi_template (cpu_list: str, plic_list, sswi_list, mtimer_list, mswi_list,
 
         mswi0: mswi@4400000 {{
           #interrupt-cells = <0>;
+          #address-cells = <0>;
           interrupt-controller;
           interrupts-extended = {mswi_list};
           reg = <0x4400000 0x4000>;