Define the iWave RainboW-G22D board dependent part of the Ethernet
AVB device node.

On some older versions of the platform (before R4.0) the phy address
may be 1 or 3. The address is fixed to 3 for R4.0 onwards (which
will be the first mainstream release), hence using 3 in the dts.
Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Signed-off-by: Chris Paterson <chris.paterson2@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>