dm: net: fec: Add .read_rom_hwaddr

Add .read_rom_hwaddr on dm eth_ops.

Cc: Stefano Babic <sbabic@denx.de>
Cc: Matteo Lisi <matteo.lisi@engicam.com>
Cc: Michael Trimarchi <michael@amarulasolutions.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>