Support to build conmon for ppc64le

[kishen-v]

Support for building conmon for ppc64le architecture, based on Add arm64 static build binary #239.

Reference:
The job make bundles fails in cri-o, due to the non availability of conmon binary for ppc64le architecture. -https://github.com/cri-o/cri-o/actions/runs/4933971318/jobs/8818878101?pr=6823
Support cri-o for ppc64le - cri-o/cri-o#6823

The nix build instructions had been validated locally.

[kishen-v]

/cc @saschagrunert. PTAL. :)
I did come across a comment which discussed about pre-populating cache. Please let me know if there's something to be done on similar lines for this PR.

Thanks in advance.

Considering our experience on the podman repo, would it make sense to go straight to the cachix solution here as well?

Yeah I think using cachix is a good move forward here. I'll pre-populate the conmon cache and come back to the CI if that is done. 👍

[saschagrunert]

Code LGTM, we should update the nixpkgs since it has some time but this can be another PR.

Binary looks good:

conmon: ELF 64-bit LSB executable, 64-bit PowerPC or cisco 7500, OpenPOWER ELF V2 ABI, version 1 (SYSV), statically linked, for GNU/Linux 2.6.32, stripped