tracking "easy" updates and improvements (for patch release 2.8.1?)

[ngam]

Comment:

We should do these in a build right after 2.8.0 (there will likely be 2.8.1 and 2.9.0 very soon). Feel free to edit and add the other outstanding migrations. I believe the ones below are relatively straightforward (the xla one may add some time to the compilation, but we will see)

• implement CPU_COUNT in bazel? #230: incorporate ${CPU_COUNT}
• Not a really a bug, but let's enable XLA in the builds going forward #223: add xla support
• Adding tensorflow-io-gcs-filesystem to the build recipe #206: add tf-io

[ngam]

Note: tf-io should be done separately. It is complicated...