configs: stm32mp1: Restore boot SPL from sdcard for stm32mp15

Restore boot SPL from sdcard for STM32MP1 platforms.

Fixes: 2a00d73d ("spl: mmc: Try to clean up raw-mode options")

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>