anv_icd.py: improve reproducible builds

Sort the output to ensure build reproducibility

Signed-off-by: Maxin B. John <maxin.john@intel.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Fixes: 0ab04ba9 ("anv: Use python to generate ICD json files")
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
(cherry picked from commit 8116b917)