sysbuild: ExternalZephyrProject_Add() cannot cope with hwmv2 board and revision

[nordicjm]

Describe the bug
This function takes a board and a board revision, which it then uses to construct a string which is provided to the target image, this works fine for HWMv1 boards, but fails for HWMv2 boards, because it places it at the end, whereas in HWMv2 the version goes after the board name, before the SoC

Expected behavior
Feature to work

Impact
Showstopper

Environment (please complete the following information):

• Commit SHA or Version used: main and v3.7-branch