kconfig: qconf: revive help message in the info view

Since commit 68fd110b ("kconfig: qconf: remove redundant help in
the info view"), the help message is no longer displayed.

I intended to drop duplicated "Symbol:", "Type:", but precious info
about help and reverse dependencies was lost too.

Revive it now.

"defined at" is contained in menu_get_ext_help(), so I made sure
to not display it twice.

Fixes: 68fd110b ("kconfig: qconf: remove redundant help in the info view")
Reported-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>