ata: qcom: Add device tree bindings information

Add device tree binding for Qualcomm AHCI SATA controller and specifically
the sata controller on the IPQ806x family of SoCs.

We can utilize the "generic-ahci" platform driver with the addition of the
sata phy to enable SATA support on Qualcomm SoCs with AHCI controllers.

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