dt-bindings: net: dsa: sja1105: add SJA1110 bindings

There are 4 variations of the SJA1110 switch which have a different set
of MII protocols supported per port. Document the compatible strings.

Also, the SJA1110 optionally supports 2 internal MDIO buses for 2
different types of Ethernet PHYs. Document a container node called
"mdios" which has 2 subnodes "mdio@0" and "mdio@1", identifiable via
compatible string, under which the driver finds the internal PHYs.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>