cros-firmware_setup_source: Allow multiple srcuri files

Handle multiple srcuri files for the firmware.
This allows per-project srcuri files, which removes the
need for manual editing of the srcuri files when updating the
files (scripts can overwrite each project's srcuris file
without touching other projects).

BUG=b:254170609
TEST=update_program_fw of craask

Change-Id: Ia6e3dc248ac7e20b13e903a7ad109283268d4497
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/3961076
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Tested-by: Andrew McRae <amcrae@google.com>
Commit-Queue: Andrew McRae <amcrae@google.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Sam McNally <sammc@chromium.org>
(cherry picked from commit 61f4fe7076ad9b2c0b63c60288e26da00b116be4)
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/4052288
Tested-by: Bruce Goodwin <bgoodwin@chromium.org>
Commit-Queue: Benjamin Gordon <bmgordon@chromium.org>
Auto-Submit: Bruce Goodwin <bgoodwin@chromium.org>
Reviewed-by: Benjamin Gordon <bmgordon@chromium.org>
1 file changed