binman: Correct testSplNoDtb() and Tpl also

binman: Correct testSplNoDtb() and Tpl also

These two tests require an ELF image so that symbol information can be
written into the SPL/TPL binary. At present they rely on other tests
having set it up first, but every test must run independently. This can
cause occasional errors in CI.

Fix this by setting up the required files, as other tests do.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>