Add arm64 to libpng build configuration.
Add arm64 to libpng build configuration.

In libpng build option, neon files were missing for arm64,
add "arm64" option to libpng build configuration.

BUG=angleproject:4026

Change-Id: I38280c8089be93de224959583091f3a151f94ab0
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1940017
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Commit-Queue: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>

ppy/angle,ppy/angle,ppy/angle,ppy/angle