Image 0 did not work. We now get rid of bootloader_backup_irq_table and
do this manually: We may not write to address 0 while an image is
running. So for image 0 we write the lower 8 pages to the backup
address. For all other images (ony image 1 currently) we write to
*both*, the original address *and* the backup address. This is done
because some addresses in the lower 8 pages *are* used at the original
address and the bootloader doesn't (want to) know which addresses are
which.
There are more safeguards now: We refuse to write to the active or
boot_next image (if boot_next is not boot_default). We mark the uploaded
partition as not ok.
Needs latest bootloader with commit ID a5771ae033b57.
