drivers: flash: stm32 ospi drivers with Memorymapped mode

Enable the MemoryMapped Mode for the stm32 octoFlash driver
Configure the Flash in MemoryMapped to use in XiP mode.
With this mode the erase and write are not supported.
Address and size are given by the DTS register property.

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