[Piglit] Adding GLES1/2 enums to piglit-dispatch.

[Eric Anholt]

This is the second digestible chunk of my gles2 branch: Adding the
enums from GLES1/2 from the enum.spec, in addition to the set we're
getting from enumext.spec.  It's on the "enums" branch of my piglit
tree, and the gles2 branch has also been updated.

It would be awesome if someone would grab the task of code-generating
a single piglit-util-gl-enum.c out of the result of this.