How do we handle HIP/ROCm support?

[jaycedowell]

Some work has been done on this at https://github.com/ADACS-Australia/bifrost/tree/hipify but we should think about merging this in here. Things to think about:

• What all do we need to do to bring this up to master?
• How complete does HIP/ROCm support need to be?
• How will we test this code base?

[jaycedowell]

I've created a test PR at #230 to see what this would even look like.