doc: add ability to generate PDF

This adds new targets to generate build documentation through
LaTEX to PDF.

There are a few notes:

1. pdflatex complains about the tex file generated by doxygen
   so it needs to be fixed with a Python script before feeding
   in through pdflatex.

2. SVG files are not recognized by pdflatex so they are converted
   to known good format on the fly, only for producing PDF. This
   uses the libRSVG's rsvg-convert tool.

Relates to #6782.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>