stm32mp: stm32prog: Remove fsbl_nor_detected from stm32prog_data struct

stm32mp: stm32prog: Remove fsbl_nor_detected from stm32prog_data struct

No more need to test if a fsbl partition is present on NOR when booting
from serial or USB. Now MTD devices are automatically populated with
partition information found in DT. Remove fsbl_nor_detected boolean from
stm32prog_data struct and all code using it.

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