ahci-imx: Port to library-ised ahci_platform

This avoids the ugliness of creating a nested platform device from probe.

While moving it around anyways, move the mk6q phy init code from probe
to imx_sata_enable, as the phy needs to be re-initialized on resume too,
otherwise the drive won't be recognized after resume.

Tested on a wandboard i.mx6 quad.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>