test: cmd: fdt: Add list of remaining missing tests

Add list of missing tests for the 'fdt' command, currently
the missing sandbox tests are only 'fdt boardsetup' and
'fdt checksign' .

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Simon Glass <sjg@chromium.org>