ata_piix: Add device ID for ICH4-L

ICH4-L is a variant of ICH4 lacking USB2 functionality and with some
different device IDs.

It is documented in Intel specification update 290745-025, currently
at <http://www.intel.com/assets/pdf/specupdate/290745.pdf

>, and is
included in the device ID table for piix.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>