Detach of-mdio dependency from stmmac-core kmod to fix support for
x86_64 target. This target doesn't use OpenFirmware infrastructure and
stmmac-core for the dwmac-intel driver doesn't depends on it.
Add kmod-of-mdio to any other user of stmmac-core as it's not inherit
from stmmac-core anymore.
Fixes: #14209
Fixes: 4b4c940fbc ("x86: Add kmod-dwmac-intel")
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
8fc954aeb7