docs: kfigure.py: Don't warn of missing PDF converter in 'make htmldocs'

SVG -> PDF conversion is not required in "make htmldocs".
It is pointless to always warn of a missing converter.
Demote the log message in setupTools() to verbose.

For "make pdfdocs" (or "make latexdocs"), promote the dynamic
message of "include SVG raw" to a warn.
Expand the message and recommend installing Inkscape or
ImageMagick.

Fixes: 8ccd05697a9d ("docs: sphinx/kfigure.py: Use inkscape(1) for SVG -> PDF conversion")
Signed-off-by: Akira Yokosawa <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: Mauro Carvalho Chehab <[e-mail]>
Cc: [e-mail]
Acked-by: Mauro Carvalho Chehab <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/sphinx/kfigure.py

···
         if convert_cmd:
             kernellog.verbose(app, "use convert(1) from: " + convert_cmd)
         else:
-            kernellog.warn(app,
+            kernellog.verbose(app,
                 "Neither inkscape(1) nor convert(1) found.\n"
                 "For SVG to PDF conversion, "
                 "install either Inkscape (https://inkscape.org/) (preferred) or\n"
···
 
         if translator.builder.format == 'latex':
             if not inkscape_cmd and convert_cmd is None:
-                kernellog.verbose(app,
-                                  "no SVG to PDF conversion available / include SVG raw.")
+                kernellog.warn(app,
+                                  "no SVG to PDF conversion available / include SVG raw."
+                                  "\nIncluding large raw SVGs can cause xelatex error."
+                                  "\nInstall Inkscape (preferred) or ImageMagick.")
                 img_node.replace_self(file2literal(src_fname))
             else:
                 dst_fname = path.join(translator.builder.outdir, fname + '.pdf')