Build for 32-bit arm v7

[Josua-SR]

Description

Add support for the 32-bit arm v7 architecture for both native and cross builds.

This change is the second step to https://github.com/projectcalico/go-build/pull/100 in making all of calico buildable for armv7. It is currently in experimentation state since I am not familiar with the design decisions impacting overall calico build processes.

Todos

• [ ] generalize cross build steps
• [ ] Unit tests (full coverage)
• [ ] Integration tests: planned
• [ ] Documentation
• [ ] Backport --> Not needed

[CLAassistant]

All committers have signed the CLA.

[caseydavenport]

/sem-approve