sandbox_spl: Restrict use of UPL when not enabled

With sandbox_spl we want to use the file-based boot in CI, so that this
flow is tested. The recent UPL change enabled booting via that method,
thus overriding the file-based boot.

Correct this by using UPL only when the --upl flag is given.

Signed-off-by: Simon Glass <sjg@chromium.org>
Fixes: 91fde8e1764 ("sandbox: Add an SPL loader for UPL")
1 file changed