[CLUSTER] Add `FEATURE-APPEND`

This cluster adds to `local.conf` a variable with `+=` assignment.

Signed-off-by: Nicola Sparnacci <nicola.sparnacci@seco.com>

src/seco_config_clusters.py

@@ -13,6 +13,7 @@ CONFIG_CLUSTERS = {
     "CONFIG_ARCH":           [ssa.do_nothing],
     "CONFIG_OS-DISTRO":      [ssa.replace_in_local_conf],
     "CONFIG_MACH":           [ssa.replace_in_local_conf, ssa.check_machine_conf],
+    "CONFIG_FEATURE-APPEND": [ssa.add_append_to_local_conf],
     "CONFIG_FEATURE":        [ssa.add_to_local_conf],
     "CONFIG_LAYERS":         [ssa.add_to_bblayers_conf],
     "CONFIG_FLAVOUR":        [ssa.add_bblayers_conf_cleaos_and_arch],