Add O AVD files

Adds the textpb file for generating an x86 O AVD and adds it to the list
of AVDs to generate on the builder.

Bug: 1145728
Change-Id: I3c5b69a5c2ac125b6961e1c36a2980253d671344
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2580738
Reviewed-by: Haiyang Pan <hypan@google.com>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#835251}