ARM64 parallel builds
- [x] closes #36719 
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [x] whatsnew entry

Seems to have gotten build from > 1 hr to ~ 38 min. 
thanks @lithomas1 yes this looks great!

 Hi!
Actually this PR changed from ARM64 to AMD64. See https://travis-ci.com/github/pandas-dev/pandas and expand `Build system information` . There you will see `OS/Arch:           linux/amd64`. The label "arm64-graviton2" is a known bug but Travis people don't want to fix it.

https://blog.travis-ci.com/2020-09-11-arm-on-aws, section "Quick tips" says: `You have to explicitly set virt: and group: keys to invoke the AWS Graviton2 CPU. Otherwise, your builds will be routed to the Travis CI default amd64 environment.` wow that's a crazy bug

cc @lithomas1  A fix is proposed with https://github.com/pandas-dev/pandas/pull/40959