pata_marvell: Add support for 88SE91A0, 88SE91A4

This patch enables support for Marvell IDE PATA controllers found on
Asus P8P67LE motherboard.

The formatting has been corrected and I also received a report from two
users of this motherboard that the patch works.

Signed-off-by: Paweł Drewniak <czajernia@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>