boards: arm: stm32h747i disco board enables QSPI interface

The stm32h474i_disco has a twin NOR flash made of two
MT25QL512 64MBytes quad-NOR devices.
Here, the partition is fully adressing the memory size.
The 1st NOR device is selected (U3 on the schematics).

Signed-off-by: Francois Ramu <francois.ramu@st.com>