dts: arm: st: move can2 definition to stm32h7.dtsi

All STM32H7 variants seems to have two fd-can interfaces available. Add
a can2 definition in stm32h7.dtsi, drop the current one in
stm32h723.dtsi. Also drop the override of address/size cells, this node
is not supposed to have any child node so they are not needed.

Signed-off-by: Fabio Baltieri <fabio.baltieri@gmail.com>