arm: socfpga: vining: Let DWMAC configure PHY reset GPIO

The DM DWMAC driver is perfectly capable of configuring the ethernet
PHY reset GPIO, let the driver do it instead of doing it in the board
file.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Siew Chin Lim <elly.siew.chin.lim@intel.com>
Cc: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Cc: Tien Fong Chee <tien.fong.chee@intel.com>