ata: ahci_platform: Update DT compatible list

The ahci_platform driver supports "snps,dwc-ahci".
Add this to the DT binding information.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Reviewed-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>