kconfig: gconf: rename gconf.glade to gconf.ui

The next commit will convert this file to GtkBuilder format. Rename
it in advance to reflect the intended format.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>