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: 8ccd0569 ("docs: sphinx/kfigure.py: Use inkscape(1) for SVG -> PDF conversion")
Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: linux-doc@vger.kernel.org
Acked-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Link: https://lore.kernel.org/r/c80e1481-10d4-7151-fe59-e846259eb0d4@gmail.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>