soc: st: stm32 Kconfig to retrieve the external Flash Base address

This commit is retrieving the config FLASH_BASE_ADDRESS
from the XSPI node of the stm32 device dtsi <reg> property of the
"st,stm32-xspi" node. For example the CONFIG_FLASH_BASE_ADDRESS
 is 0x90000000 and application is linked for that address.
Size is given by the size property of the "st,stm32-xspi-nor" node.

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