ARM: dts: stm32: Configure Buck3 voltage per PMIC NVM on Avenger96

The Avenger96 board comes in multiple regulator configurations.
 - rev.100 or rev.200 have Buck3 preconfigured to 3V3 operation on
   boot and contains extra Enpirion EP53A8LQI DCDC converter which
   supplies the IO. Reduce Buck3 voltage to 2V9 to not waste power.
 - rev.200L have Buck3 preconfigured to 1V8 operation and have no
   Enpirion EP53A8LQI DCDC anymore, the IO is supplied from Buck3.

Configure the Buck3 voltage on this board per PMIC NVM settings and
update buck3 voltage limits in DT passed to OS before booting OS to
prevent potential hardware damage.

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: Patrick Delaunay <patrick.delaunay@foss.st.com>