It is annoying to have disk images in the source directory since it
clutters up the working space.
Remove cur_dir=True from DiskHelper calls so disk images are written to
the persistent-data directory instead.
Move scsi.img too (used by the bootstd tests) and mmc6.img (used by the
MBR tests.
Add a few comments as to where the images are used.
This keeps the source tree clean and puts disk images in the same place
as other test data.
Co-developed-by: Claude Opus 4.5 <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>
3f133727bf