scripts: sphinx-pre-install: improve openSuse Tumbleweed check

scripts: sphinx-pre-install: improve openSuse Tumbleweed check

Currently, with openSUSE Tumbleweed 20200303, it keeps
recommending this forever:

	sudo zypper install --no-recommends rsvg-view

This dependency will never be fulfilled there, as the package
now is named as on other distros: rsvg-convert.

So, improve the detection to avoid such issue.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/c3774f72ac36c5e5b5f446ae5db5b795d1f274f4.1586883286.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>