dt-bindings: net: mscc-miim: add lan966x compatible

The MDIO controller has support to release the internal PHYs from reset
by specifying a second memory resource. This is different between the
currently supported SparX-5 and the LAN966x. Add a new compatible to
distinguish between these two.
Signed-off-by: Michael Walle <michael@walle.cc>
Acked-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/devicetree/bindings/net/mscc-miim.txt

@@ -2,7 +2,7 @@ Microsemi MII Management Controller (MIIM) / MDIO
 =================================================
 
 Properties:
-- compatible: must be "mscc,ocelot-miim"
+- compatible: must be "mscc,ocelot-miim" or "microchip,lan966x-miim"
 - reg: The base address of the MDIO bus controller register bank. Optionally, a
   second register bank can be defined if there is an associated reset register
   for internal PHYs