The dwmac-socfpga driver needs to control the reset usually managed
by the core driver to set the PHY mode. Take a copy of the reset
handle from core priv data so it can be used by the driver later.

This also allow us to move reset handling into socfpga_dwmac_setup()
where the code that needs it is located.
Signed-off-by: NJoachim Eastwood <manabian@gmail.com>
Tested-by: NMarek Vasut <marex@denx.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>