docs: Start mathifying TGSI insts.

src/gallium/docs/source/conf.py

@@ -22,7 +22,7 @@ import sys, os
 
 # Add any Sphinx extension module names here, as strings. They can be extensions
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
-extensions = []
+extensions = ['sphinx.ext.pngmath']
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']