ARM: stm32: Add missing header for save_boot_params

The get_stm32mp_rom_api_table() function is defined in sys_params.h ,
add the missing header to avoid compiler warning.

Fixes: dbeaca79 ("ARM: stm32: Factor out save_boot_params")
Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>