ahci: imx: add the imx6qp ahci sata support

- Regarding to imx6q ahci sata, imx6qp ahci sata
has the reset mechanism. Add the imx6qp ahci sata
support in this commit.
- Use the specific reset callback for imx53 sata,
and use the default ahci_ops.softreset for the others.

Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
Signed-off-by: Tejun Heo <tj@kernel.org>