Docs: Add cell gen to makefile

Generate in a temp directory and use `rsync -rc` to only update rst files that have changed.  This prevents sphinx from having to re-generate every cmd/cell page any time the git sha changes.
Also change cmd gen to match.

Makefile

@@ -974,8 +974,17 @@ endif
 
 # also others, but so long as it doesn't fail this is enough to know we tried
 docs/source/cmd/abc.rst: $(TARGETS) $(EXTRA_TARGETS)
-	mkdir -p docs/source/cmd
-	./$(PROGRAM_PREFIX)yosys -p 'help -write-rst-command-reference-manual'
+	$(Q) mkdir -p docs/source/cmd
+	$(Q) mkdir -p temp/docs/source/cmd
+	$(Q) cd temp && ./../$(PROGRAM_PREFIX)yosys -p 'help -write-rst-command-reference-manual'
+	$(Q) rsync -rc temp/docs/source/cmd docs/source
+	$(Q) rm -rf temp
+docs/source/cell/add.rst: $(TARGETS) $(EXTRA_TARGETS)
+	$(Q) mkdir -p docs/source/cell
+	$(Q) mkdir -p temp/docs/source/cell
+	$(Q) cd temp && ./../$(PROGRAM_PREFIX)yosys -p 'help -write-rst-cells-manual'
+	$(Q) rsync -rc temp/docs/source/cell docs/source
+	$(Q) rm -rf temp
 
 PHONY: docs/gen_examples docs/gen_images docs/guidelines docs/usage docs/reqs
 docs/gen_examples:

docs/Makefile

@@ -47,7 +47,7 @@ help:
 .PHONY: clean
 clean: clean-examples
 	rm -rf $(BUILDDIR)/*
-	rm -rf source/cmd util/__pycache__
+	rm -rf source/cell source/cmd util/__pycache__
 	$(MAKE) -C source/_images clean
 
 .PHONY: html