[PATCH] sata_promise: Add PDC40519 id

The Promise TX4200 is a 4-port SATA controller based on the PDC40519 chip. It
meets the description of the 20319, so just a simple ID needs to be added to
support this hardware. Thanks to Martin Povolný for testing.

Signed-off-by: Daniel Drake <dsd@gentoo.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>