ata: make the ata_piix driver using new SATA framework

original ata_piix driver is using IDE framework, not real
SATA framework. For now, the ata_piix driver is only used
by x86 sc520_cdp board. This patch makes the ata_piix driver
use the new SATA framework, so

- remove the duplicated command stuff
- remove the CONFIG_CMD_IDE define in the sc520_cdp.h
- add the CONFIG_CMD_SATA define to sc520_cdp.h

Signed-off-by: Dave Liu <daveliu@freescale.com>