scripts/dts: Fix issue in label generation of registers

If we have something like:

       #address-cells = <1>;
       #size-cells = <0>;

       intc: ioapic@fec00000  {
	       compatible = "intel,ioapic";
	       reg = <0xfec00000 0x100000>;
       };

We should generate:

DT_INTEL_IOAPIC_FEC00000_BASE_ADDRESS_0
DT_INTEL_IOAPIC_FEC00000_BASE_ADDRESS_1

Instead we generated:

DT_INTEL_IOAPIC_FEC00000_BASE_ADDRESS
DT_INTEL_IOAPIC_FEC00000_BASE_ADDRESS_1

This was due to logic deciding if '_0' should be used not taking into
account #address-cells & #size-cells correctly.

Fixes: #16296

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>