xilinx: common: Add support for DM_I2C zynq_board_read_rom_ethaddr()

It is much easier to point to eeprom which stores information like MAC
address directly via DT. eeprom which contains this information is
pointed by /chosen/xlnx,eeprom parameter.

For example:
        chosen {
                bootargs = "earlycon";
                stdout-path = "serial0:115200n8";
+               xlnx,eeprom = &eeprom;
        };

Signed-off-by: Michal Simek <michal.simek@xilinx.com>