ata: sata_dwc_460ex: add phy support

This adds support for powering on an optional PHY when activating the
device.

Tested-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: Mans Rullgard <mans@mansr.com>
Signed-off-by: Tejun Heo <tj@kernel.org>