[PATCH] libata: use SATA speed down in ata_drive_probe_reset()

Make ata_drive_probe_reset() use SATA SPD configuration.  Hardreset
will be force if speed renegotiation is necessary.  Also, if a
hardreset fails, PHY speed is stepped down and hardreset is retried
until the lowest speed is reached.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>