[CUDA][HIP] Reorganize options for documentation

Reorganize options and group them as "Common Offloading options",
"CUDA options" and "HIP options", so that they will be grouped
together like "OpenCL options" and "SYCL options" in
https://clang.llvm.org/docs/ClangCommandLineReference.html

Reviewed by: Joseph Huber, Fangrui Song

Differential Revision: https://reviews.llvm.org/D156886