ahci: add DT binding for Calxeda AHCI controller

Add devicetree match table to ahci platform driver for Calxeda Highbank
AHCI controller.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Jeff Garzik <jgarzik@pobox.com>
Cc: linux-ide@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: devicetree-discuss@lists.ozlabs.org