dt-bindings: ata: add compatible string for iProc AHCI controller

The Broadcom iProc SoCs have AHCI compliant SATA controller. This
patch adds common compatible string for AHCI SATA controller on
iProc SoCs.
Signed-off-by: Anup Patel <anup.patel@broadcom.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

Documentation/devicetree/bindings/ata/ahci-platform.txt

@@ -10,6 +10,7 @@ PHYs.
 Required properties:
 - compatible        : compatible string, one of:
   - "allwinner,sun4i-a10-ahci"
+  - "brcm,iproc-ahci"
   - "hisilicon,hisi-ahci"
   - "cavium,octeon-7130-ahci"
   - "ibm,476gtr-ahci"