kconfig: Update Kconfiglib and use new helpers in kconfig.py

Update Kconfiglib, menuconfig, and guiconfig to upstream revision
faa1d21998, mostly to get this commit in:

    Add public helpers for generating "<name> (defined at ...)" strings

    Have Symbol/Choice.name_and_loc return strings like

        "MY_SYM (defined at foo:1, bar:2)"
        "<choice> (defined at foo:4)"

    I've added a function like that in at least four different scripts
    now, so that's probably a sign that it's a worthwhile helper.

    Clean up the tests/Klocation tests a bit while adding tests.

Use the new helper to simplify kconfig.py a bit. Also clean it up a bit
by removing some unused stuff.

Some other minor improvements are included as well, e.g. to make
menuconfig/guiconfig give more helpful errors on invalid arguments.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>