qconfig: Move converting config args to the top

qconfig: Move converting config args to the top

Move this check to the top, so it happens always. There is no harm to
doing this earlier and it separates the setup from actual program logic.

Update the arg rather than adding a new variable, with the new variable
only created when moving or building, since it is used more heavily.

Signed-off-by: Simon Glass <sjg@chromium.org>