kconfig: change nonint_oldconfig to listnewconfig

Rename to a name that better match the other kconfig targets.

listnewconfig shall read as:

- list new options compared to current configuration

New options are now written to stdout so one can redirect the output.

Do not exit with an error code if there is new options.

These are feature changes compared to the original
nonint_oldconfig - but as this feature has not yet been in a
released kernel it should not matter.

It is still possible to do:

make listnewconfig
lookup new config options in Kconfig*
edit .config

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Aristeu Rozanski <aris@redhat.com>
Acked-by: Aristeu Rozanski <aris@redhat.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>