dts: arm: st: stm32h5 serie has xspi node

Define the xspi node instead of ospi. Note that RCC CCIPR4 register
keeps the OCTOSP1 for clock domain selection.
Change the header file to xspi for the stm32 devices with xspi
peripheral. Keep the flash_controller/ospi.h for bindings compatibilty.

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