CUDA: Get PETSc to compile with CUDA 11.
CUSPARSE has changed significantly in CUDA 11. This has lead to a lot of broken code.
This merge request is not a full fix, but at least ensures that PETSc compiles with other GPU features enabled. To achieve this, the AIJCUSPARSE class is effectively disabled.
I estimate that a full fix requires a few days (maybe 2-3) of concentrated effort working along the CUSPARSE documentation https://docs.nvidia.com/cuda/cusparse/index.html