doc: convert image extensions to wildcard

doc: convert image extensions to wildcard

Changed all image.svg and image.png extensions to image.*
This allows Sphinx to decide the appropriate image type
from the available image options.

In case of PDF, SVG images are converted and Sphinx must pick
the converted version.

Signed-off-by: John McNamara <john.mcnamara@intel.com>
Acked-by: Bernard Iremonger <bernard.iremonger@intel.com>