net: designware: socfpga: Add Arria10 extras

Add wrapper around the designware MAC driver to handle the SoCFPGA
specific configuration bits. On Arria10, this is configuration of
syscon phy_intf.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Chin Liang See <chin.liang.see@intel.com>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Ley Foon Tan <ley.foon.tan@intel.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>