Adding code to run on Powersystem

[genisysram]

Hi
Here is my contribution to your code, its working good on powersystems.

Thanks for the code, its working good.

What do these changes do?

Added Architecture "ppc64le"

Are there changes in behavior for the user?

No

[thaJeztah]

This repository is moving away from Travis, so this would probably have to be re-written for GitHub actions (after #78 is merged)

[kzys]

And GitHub Actions don't support ppc64le... Does it make sense to cross-compile ttrpc in GitHub Actions for different platforms/architectures?

[dmcgowan]

a PR to enabling cross compile would be OK