MAINTAINERS: Update Kconfig section

Masahiro Yamada stepped down as Kbuild and Kconfig maintainer in
commit 8d6841d5cb20 ("MAINTAINERS: hand over Kbuild maintenance"),
leaving Kconfig officially orphaned and handing Kbuild over to Nicolas
and myself. Since then, there have been a few simple patches to Kconfig
that have ended up on the linux-kbuild mailing list without clear
direction on who will take them, as they are not really sent to anybody
officially, although the list is obviously watched by the Kbuild
maintainers.

Make Nicolas and I official maintainers of Kconfig in "Odd Fixes"
status, similar to Kbuild, so that the subsystem has clear points of
contact for contributors, even if significant contributions may not be
accepted.

Additionally, add the Kbuild tree to this section.

Acked-by: Nicolas Schier <nsc@kernel.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://patch.msgid.link/20251023-update-kconfig-maintainers-v1-1-0ebd5b4ecced@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>