ARM: dts: stm32: Move vdd_io extras into Avenger96 extras

The vdd_io regulator is present only on DHCOR SoM configured for 1V8 IO,
as populated on Avenger96, but not present on 3V3 DHCOR SoM. Move these
extras to Avenger96 u-boot DT extras.

Fixes: 3919aa17 ("ARM: dts: stm32: Add DFU support for DHCOR recovery")
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>