uboot-imx

sandbox: Stop printing platdata at the start of SPL

Currently we have code which prints out platform data at the start of SPL.
Now that we have tests for dtoc this is probably not necessary. Drop it.
Update test_ofplatdata to check for empty output since it is useful to
check that sandbox_spl works as expected.

Signed-off-by: Simon Glass <sjg@chromium.org>