ahci-vt8251

* requires hardreset after PHY status change

* doesn't clear BSY on signature FIS after hardreset

* needs SError cleared for the port to operate after hardreset

This patch implements ahci_vt8251_hardreset() and sets
ATA_FLAG_HRST_TO_RESUME to handle the above behaviors.  This fixes EH
including hotplug on vt8251.
Signed-off-by: NTejun Heo <htejun@gmail.com>
Signed-off-by: NJeff Garzik <jeff@garzik.org>