WHILE AMERICAN AUDIENCES continue to boogie as though it were still 1968, London has been overrun by pop maniacs, raising the ghost of Carnaby Street and blasting slogans of teenage rampage into each other's ears. Suzi Quatro is the glittering sex queen presiding over that scene. A short, trim woman from Detroit who moved to England after nine unsuccessful years in the American music business, her black-leather-and-chains unisex image has somehow captured the imagination of Britain's glam generation.