MAINTAINERS: take over Kconfig maintainership

I have recently picked up Kconfig patches to my tree without any
declaration.  Making it official now.

Signed-off-by: Masahiro Yamada <[email protected]>
Acked-by: Linus Torvalds <[email protected]>

Author: masahir0y

MAINTAINERS

@@ -7600,8 +7600,10 @@ F:	mm/kasan/
 F:	scripts/Makefile.kasan
 
 KCONFIG
+M:	Masahiro Yamada <[email protected]>
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git kconfig
 L:	[email protected]
-S:	Orphan
+S:	Maintained
 F:	Documentation/kbuild/kconfig-language.txt
 F:	scripts/kconfig/