sata_fsl: Add power mgmt support

Signed-off-by: Dave Liu <daveliu@freescale.com>
Signed-off-by: Liu Yu <yu.liu@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>