MINNEAPOLIS — SuperValu said Tuesday it’s looking to spin off its heavy-discount Save-A-Lot supermarket chain into a separate company.Save-A-Lot is a national chain with 1,300 stores — including one in Cedar Rapids — and is considered Supervalu’s crown jewel by some stock analysts. Save-A-Lot makes up about one-quarter of the company’s sales.SuperValu, based in suburban Minneapolis, has set no timetable for the disposition of St.