[PATCH] sata_promise: Add PDC40718 id

Otto Meier recently submitted a patch to support the PDC40718 chip (marketed
as SATA300 TX4, a 4-port SATA controller).

Signed-off-by: Otto Meier <gf435@gmx.net>
Signed-off-by: Daniel Drake <dsd@gentoo.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>