net: ethernet: stmmac: Fix altr_tse_pcs SGMII Initialization

Fix NETDEV WATCHDOG timeout on startup by adding missing register
writes that properly setup SGMII.

Signed-off-by: Thor Thayer <thor.thayer@linux.intel.com>
Acked-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>