sata_dwc_460ex: support hardreset

The hardreset operation is currently not supported. This causes
sometime the SATA driver does cause kernel crash because of
none-determined state.a This patch will fix the issue.

Signed-off-by: Thang Q. Nguyen <tqnguyen@apm.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>