stallion: final cleanup

Support for the Stallion multiport serial drivers was removed in v3.1.
Clean up their last references in the tree: mainly an outdated Kconfig
entry and unneeded documentation.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>