boards: arm: stm32 disco kit has ospi nor flash node

Define the reg and size property for the stm32u585 and stm32l562
disco kit.
Refer to the dts/bindings/flash_controller/st,stm32-ospi-nor.yaml.
The stm32l562 reads the sfdp table from the flash itself.

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