With the introduction of ABI-specific build targets (zlib), the script
generate_android_bp.py needs to be updated to consume ABI-specific gn
descriptions and generate ABI-specific build rules for each target.

The roll_aosp.sh script was updated to generate ABI-specific gn
descriptions for each:
    arm
    arm64
    x86
    x64

Bug: b/160727922
Test: Manual script execution and building in AOSP
Change-Id: I459b388176f8fcc010f9f5668535d941b931cdd4
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2285272
Commit-Queue: Tim Van Patten <timvp@google.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>