Kconfig: Change symbol override from warning to notice

Kconfig: Change symbol override from warning to notice

Overriding symbols within a .config is pretty common when doing
automated builds with various different options.  The warning
text makes it sound like this is an issue, so change it to say
'notice' instead.  We could get rid of it completely, but it's
not a bad thing to know that we have two copies of the same symbol
in the .config.

BUG=chrome-os-partner:54059
TEST=copy a disabled kconfig option to the end and set it to y.
See notice text instead of warning.

Change-Id: I9f575b2275233f638e42676263348c807e6515bd
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/16691
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>