arm: stm32: Enable TCP, IPv6, wget on DH STM32MP15 DHSOM

Enable support for TCP protocol, wget, and IPv6 on this platform.
The former two allow users download payload into the U-Boot from
a web server, which may be more convenient or easier to set up
than TFTP server. The later is enabled to future proof the IP
stack on this platform.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>