ata: ahci_imx: allow hardware parameters to be specified in DT

Various SATA phy parameters are board specific, and therefore need to
be configured.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Reviewed-by: Shawn Guo <shawn.guo@freescale.com>
Signed-off-by: Tejun Heo <tj@kernel.org>