test: spl: Support testing LEGACY_LZMA filesystem images

These will soon be supported, so we need to be able to test it. Export the
lzma data and generally use the same process in spl_test_mmc_fs as
do_spl_test_load.  If we end up needing this in third place in the future,
it would probably be good to refactor things out.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
3 files changed