kconfig: refactor .gitignore

Add '/' prefix to clarify that the generated files exist right under
scripts/kconfig/, but not in any sub-directory.

Replace '*conf-cfg' with '[gmnq]conf-cfg' to make it explicit, and
still short enough.

Use '[gmnq]conf' to combine gconf, mconf, nconf, and qconf.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/kconfig/.gitignore

 # SPDX-License-Identifier: GPL-2.0-only
+/conf
+/[gmnq]conf
+/[gmnq]conf-cfg
 /qconf-moc.cc
-*conf-cfg
-
-#
-# configuration programs
-#
-conf
-mconf
-nconf
-qconf
-gconf