ARM: dts: stm32: Add Ethernet support on stm32h7 SOC and activate it for eval and disco boards

Synopsys GMAC 4.10 is used. And Phy mode for eval and disco is RMII
with PHY SMSC LAN8742

Signed-off-by: Christophe Roullier <christophe.roullier@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>