USB Serial Keyspan: add support for USA-49WG & USA-28XG

Add support for Keyspan adapters: USA-49WG and USA-28XG

Signed-off-by: Lucy P. McCoy <lucy@keyspan.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>