pylibfdt: Make SETUP make variable

This points to the Python setup script, since we reference it in a couple
of places.  While we're there correct two small problems:

1) setup.py is part of the checked in sources and so lives in
   $(PYLIBFDT_srcdir) not $(PYLIBFDT_objdir) [this only worked because
   those are the same by default]

2) The module itself should depend on the setup script so it is rebuilt
   if the script is changed

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Simon Glass <sjg@chromium.org>

pylibfdt/Makefile.pylibfdt

@@ -4,12 +4,14 @@
 PYLIBFDT_srcs = $(PYLIBFDT_srcdir)/libfdt.i
 PYMODULE = $(PYLIBFDT_objdir)/_libfdt.so
 
+SETUP = $(PYLIBFDT_srcdir)/setup.py
+
 define run_setup
 	VERSION="$(dtc_version)"
-	$(PYLIBFDT_objdir)/setup.py --quiet $(1)
+	$(SETUP) --quiet $(1)
 endef
 
-$(PYMODULE): $(PYLIBFDT_srcs) $(LIBFDT_archive)
+$(PYMODULE): $(PYLIBFDT_srcs) $(LIBFDT_archive) $(SETUP)
 	@$(VECHO) PYMOD $@
 	$(call run_setup, build_ext --build-lib=$(PYLIBFDT_objdir))