phy: berlin-sata: Document BG2 compatible

Berlin BG2 SATA PHY is slightly different from currently supported
BG2Q SATA PHY. Document the new compatible for BG2's PHY.
Acked-by: Antoine Ténart <antoine.tenart@free-electrons.com>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>

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

@@ -2,7 +2,9 @@ Berlin SATA PHY
 ---------------
 
 Required properties:
-- compatible: should be "marvell,berlin2q-sata-phy"
+- compatible: should be one of
+    "marvell,berlin2-sata-phy"
+    "marvell,berlin2q-sata-phy"
 - address-cells: should be 1
 - size-cells: should be 0
 - phy-cells: from the generic PHY bindings, must be 1