Documentation/sphinx: make it possible to build latexdocs without pdflatex

Building latexdocs doesn't actually require $(PDFLATEX). Move the checks
for it to the pdfdocs target which does require it, and specifically
outside of the target in order to not depend on latexdocs when we can't
build pdfdocs anyway.
Reviewed-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>
Tested-by: NMarkus Heiser <markus.heiser@darmarIT.de>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>

Documentation/Makefile.sphinx

@@ -69,15 +69,17 @@ htmldocs:
 	@$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,html,$(var),,$(var)))
 
 latexdocs:
+	@$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,latex,$(var),latex,$(var)))
+
 ifeq ($(HAVE_PDFLATEX),0)
+
+pdfdocs:
 	$(warning The '$(PDFLATEX)' command was not found. Make sure you have it installed and in PATH to produce PDF output.)
 	@echo "  SKIP    Sphinx $@ target."
+
 else # HAVE_PDFLATEX
-	@$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,latex,$(var),latex,$(var)))
-endif # HAVE_PDFLATEX
 
 pdfdocs: latexdocs
-ifneq ($(HAVE_PDFLATEX),0)
 	$(foreach var,$(SPHINXDIRS), $(MAKE) PDFLATEX=$(PDFLATEX) LATEXOPTS="$(LATEXOPTS)" -C $(BUILDDIR)/$(var)/latex)
 
 endif # HAVE_PDFLATEX