sata_dwc_460ex: add debugging options

The driver makes use of the two options (CONFIG_SATA_DWC_[V]DEBUG) to enable
the debug output but they both are absent in drivers/ata/Kconfig...

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>