HSD #14019448981: net: ethernet: altera: support phy_handle in mdio (#219)

commit 0d69f54b8a102c441e7f6cea0bab9912d7a0db9f from
https://github.com/altera-opensource/linux-socfpga.git

 socfpga-6.1.55-lts.

this patch add additional support to read phy_handle
from mdio node specified in device tree, and connect
the phy via phylink interface.

Signed-off-by: Swee Leong Ching <leong.ching.swee@intel.com>
Signed-off-by: Liwei Song <liwei.song@windriver.com>