[third_party/ffmpeg] add roll scripts for custom profiles

This CL adds python scripts for an updated roll process that supports
custom profiles. The new roll process is driven by files that
describe and enumerate the profiles. Those files will be generated
in the fuchsia main repo using GN.

This CL does not include a roll. That will happen in a subsequent CL.

Bug: 87666

Test: build change

Change-Id: I0442747b439107860605c0ba37d14015ee26ca53
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/ffmpeg/+/781083
Reviewed-by: Petr Hosek <phosek@google.com>
7 files changed