Codegen should be able to generate one DPU binary per upmem.launch

[oowekyala]

Currently the UPMEM->DPU CPP pass generates one C file with just one main function.
We need to generate one binary for each upmem.launch though. The thread count is launch-specific, needs to be passed as compiler option when compiling DPU binary.

Draft design:

• Outline all DPU kernels into single module
• Have upmem->DPU CPP generate one function for each upmem.launch
• Have a main that conditionally compiles exactly one of those functions
• The conditional compilation variables along with the thread count are written in a header comment on line 1.
• This comment is parsed by a script that then invokes the DPU compiler and generates as many binaries as there are upmem.launch blocks.
• The binary path for each launch must be passed as argument to upmemrt_dpu_alloc.