kconfig: Revert back to old behaviour pre-kconfiglib.py

Run Kconfig on every reconfigure but with different fragments
depending on the situation.

When .config is missing or when a file from merge_config_file has been
modified use the merge_config_file's as input, otherwise use .config
as input.

This should match the behaviour before kconfiglib.py was introduced
and fixes #5673.

Signed-off-by: Sebastian Bøe <sebastian.boe@nordicsemi.no>
1 file changed