Amend 64 bit blacklist.

- external/skia now builds on arm64, frameworks/base/libs/hwui
  depends on it.
- external/bluetooth/bluedroid builds on 64 bit, though there
  isn't any obvious way to test it without real hardware.
- frameworks/ml now builds, as does external/srec
- frameworks/opt, frameworks/ex and frameworks/wilhelm don't
  build because of their dependency on frameworks/av.

frameworks/av should probably be dropped out of the blacklist
and replaced by individual markers on targets that we want
for 64 bit (we don't want all of them for arm64).

Change-Id: I9735108840fcba21ac8918bedf0d6de8989de086