u-boot-iot2050: Move the tools building to the last step

So that the previous steps could use the native tools, for example,
the iot2050-sign-fw.sh could use the built native mkimage.

Signed-off-by: Baocheng Su <baocheng.su@siemens.com>

recipes-bsp/u-boot/files/rules.tmpl

@@ -22,10 +22,10 @@ override_dh_auto_build:
 	else \
 		./scripts/get_default_envs.sh >u-boot-initial-env; \
 	fi
-	$(MAKE) $(PARALLEL_MAKE) $(SET_CROSS_BUILD_TOOLS) NO_SDL=1 tools-only envtools
 	if [ -e keys ]; then \
 		tools/iot2050-sign-fw.sh keys/custMpk.pem ${FIRMWARE_SECURE_VER}; \
 	fi
+	$(MAKE) $(PARALLEL_MAKE) $(SET_CROSS_BUILD_TOOLS) NO_SDL=1 tools-only envtools
 
 override_dh_auto_install:
 	mv tools/env/lib.a tools/env/libubootenv.a