net: ethernet: Add TSE PCS support to dwmac-socfpga

This adds support for TSE PCS that uses SGMII adapter when the phy-mode of
the dwmac is set to sgmii.

Signed-off-by: Tien Hock Loh <thloh@altera.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>