docs: add poky.yaml and sphinx-static/switchers.js to "make clean"

(From yocto-docs rev: 36d1be3db5f0c9c72aafdb414916ce5abc483f43)

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/Makefile

@@ -44,7 +44,7 @@ PNGs := $(foreach dir, $(IMAGEDIRS), $(patsubst %.svg,%.png,$(wildcard $(SOURCED
 	$(SVG2PNG) --export-filename=$@ $<
 
 clean:
-	@rm -rf $(BUILDDIR) $(PNGs) $(PDFs)
+	@rm -rf $(BUILDDIR) $(PNGs) $(PDFs) poky.yaml sphinx-static/switchers.js
 
 epub: $(PNGs)
 	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)