env: Distinguish finer between source of env change

We already could tell the difference in the callback between an import
and "other" which we called interactive. Now add further distinction
between interactive (i.e. running env set / env edit / env ask / etc.
from the U-Boot command line) and programmatic (i.e. when u-boot source
calls any variant of setenv() ).

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Simon Glass <sjg@chromium.org>