configs: stm32mp1: activate Ethernet PHY Realtek

Need Realtek driver to manage in RTL8211F the configuration of the LED.
Initialize LCR (LED Control Register) to configure green LED for Link,
yellow LED for Active

Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Christophe Roullier <christophe.roullier@st.com>
Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>