Add magma-rocm packages

This is a rough outline of the magma-rocm source package. I don't expect this can be merged as-is, but it works (or at least it did when I built with -DAMDGPU_TARGETS=gfx1100, the build takes a long time with all GPUs enabled and it's possible it might exceed the 2GB limit and fail linking). Update: the library is ~1.3 GB, so it's fine.

gbp dch --nmu
./debian/rocmbuild.sh
gbp buildpackage --git-ignore-new