Adding POWER(ppc64le) architecture support

[bahetiamit]

This change adds the support for POWER (ppc64le) architecture to the image. This was tested on master branch in travis. This is an extension to #23

[barthy1]

Hi @bahetiamit ! Thank you for this PR.
Could you please share Travis build logs and link to the multi-arch image you got after the build?

[bahetiamit]

@barthy1

Please find the travis logs at - https://travis-ci.org/github/bahetiamit/git/builds/729545845 and travis built images at - https://hub.docker.com/repository/registry-1.docker.io/bahetiamit/git/tags?page=1

[barthy1]

hey @ozbillwang
I've verified that proposed code adds ppc64le arch to multi-arch apline/git images.
I also verified that resulted ppc64le image is buildable and runnable for according arch. No changes are introduced for s390x or amd64 builds.

Are you ok to merge this code?

[ozbillwang]

Thanks, @barthy1

I am fine for the change. Let's merge it.

Please confirm if you can merge it directly.

[snehlatamohite]

@bahetiamit @barthy1 - Thanks for working on this.