tools/ocaml: add 'make format' for OCaml files

Using `ocp-indent` for now to just make minimal modifications in
tabs vs spaces and get the right indentation.

This avoids perpetuating a formatting style that is inconsistent with
the rest of Xen, and that makes preparing and submitting patches more
difficult (OCaml indentation tools usually only support spaces, not tabs).

No functional change.

Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>

tools/ocaml/Makefile

@@ -34,3 +34,7 @@ build-tools-oxenstored:
 	$(MAKE) -s -C libs/xb
 	$(MAKE) -s -C libs/xc
 	$(MAKE) -C xenstored
+
+.PHONY: format
+format:
+	git ls-files '*.ml' '*.mli' | xargs -n1 ocp-indent -i