docker: add debian/tricore image

TriCore binutils is built from Bastian Koppelmann repository.

Note: There is no TriCore compiler in this image (only assembler/linker).

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
[AJB: base of Debian9, add to Makefile.include]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
diff --git a/tests/docker/Makefile.include b/tests/docker/Makefile.include
index 9d57498..74fd51c 100644
--- a/tests/docker/Makefile.include
+++ b/tests/docker/Makefile.include
@@ -63,6 +63,9 @@
 docker-image-debian-win64-cross: docker-image-debian8-mxe
 docker-image-travis: NOUSER=1
 
+# Specialist build images, sometimes very limited tools
+docker-image-tricore-cross: docker-image-debian9
+
 # Expand all the pre-requistes for each docker image and test combination
 $(foreach i,$(DOCKER_IMAGES) $(DOCKER_DEPRECATED_IMAGES), \
 	$(foreach t,$(DOCKER_TESTS) $(DOCKER_TOOLS), \