[CUDA] Handle non-CUDA devices in copy/migrate commands
[CUDA] Handle non-CUDA devices in copy/migrate commands

Still doesn't work for non-CUDA devices that aren't using host memory,
but this is a rare use case that we can ignore for now.

franz/pocl,pocl/pocl,Oblomov/pocl,pocl/pocl,franz/pocl,franz/pocl,pocl/pocl,Oblomov/pocl,Oblomov/pocl,Oblomov/pocl,rjodin/pocl,Oblomov/pocl,franz/pocl,rjodin/pocl,franz/pocl,pocl/pocl,pocl/pocl,rjodin/pocl,rjodin/pocl