arm64: dts: st: enable ethernet1 controller on stm32mp257f-ev1

arm64: dts: st: enable ethernet1 controller on stm32mp257f-ev1

ethernet1 controller is connected to the RTL8211F-CG Realtek PHY in
RGMII mode. It can either be used as a standalone Ethernet controller
or be connected to the internal TSN capable switch. For this board,
keep the standalone setup. Also enable this peripheral on the
stm32mp257f-ev1 board.

Signed-off-by: Gatien Chevallier <gatien.chevallier@foss.st.com>
Link: https://lore.kernel.org/r/20250904-mp2_ethernet-v2-3-05a060157fb7@foss.st.com
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>