fec: Move imx_get_mac_from_fuse declare to imx file

imx_get_mac_from_fuse is used to load MAC address from fuse. On imx8mp,
we have two different ENET controllers and both need to call this
function. So decouple its declare from fec driver.

Reviewed-by: Fugang Duan <fugang.duan@nxp.com>
Signed-off-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>