net: stmmac: socfpga: add additional ocp reset line for Stratix10

The Stratix10 platform has an additional reset line, OCP(Open Core Protocol),
that also needs to get deasserted for the stmmac ethernet controller to work.
Thus we need to update the Kconfig to include ARCH_STRATIX10 in order to build
dwmac-socfpga.

Also, remove the redundant check for the reset controller pointer. The
reset driver already checks for the pointer and returns 0 if the pointer
is NULL.

Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>