net: macb: Add phy address to read it from device tree

Read phy address from device tree and use it to find the phy device
if not found then search in the range of 0 to 31.

Signed-off-by: Padmarao Begari <padmarao.begari@microchip.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Bin Meng <bin.meng@windriver.com>
Tested-by: Bin Meng <bin.meng@windriver.com>