dt-bindings: phy: Document BCM7216 SATA PHY compatible string

Define "brcm,bcm7216-sata-phy" as a new compatible string for the
Broadcom SATA3 PHY.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>

Documentation/devicetree/bindings/phy/brcm-sata-phy.txt

@@ -2,6 +2,7 @@
 
 Required properties:
 - compatible: should be one or more of
+     "brcm,bcm7216-sata-phy"
      "brcm,bcm7425-sata-phy"
      "brcm,bcm7445-sata-phy"
      "brcm,iproc-ns2-sata-phy"