binman: Support ELF files for TPL

We currenty support using the ELF file in U-Boot proper and SPL, but not
TPL. Add this as it is useful both with sandbox and for CBFS to allow
adding TPL as a 'stage'.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/ftest.py b/tools/binman/ftest.py
index 6ff871b..9cec5f4 100644
--- a/tools/binman/ftest.py
+++ b/tools/binman/ftest.py
@@ -1746,6 +1746,8 @@
         """Basic test of ELF entries"""
         self._SetupSplElf()
         with open(self.TestFile('bss_data'), 'rb') as fd:
+            TestFunctional._MakeInputFile('tpl/u-boot-tpl', fd.read())
+        with open(self.TestFile('bss_data'), 'rb') as fd:
             TestFunctional._MakeInputFile('-boot', fd.read())
         data = self._DoReadFile('096_elf.dts')