isl: Replace bash generator with python generator

isl: Replace bash generator with python generator

This replaces the current bash generator with a python based generator
using mako. It's quite fast and works with both python 2.7 and python
3.5, and should work with 3.3+ and maybe even 3.2.

It produces an almost identical file except for a minor layout changes,
and the addition of a "generated file, do not edit" warning.

Cc: "12.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Dylan Baker <dylanx.c.baker@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>