Lower non-RCU macros

[PappasBrent]

Once #30 is merged, PASTA will no longer be required to lower RCU macros down to the Kernel dialect; however we will also no longer lower non-RCU macros down to the Kernel dialect either.
It will be much harder to do so since non-RCU macros like get_user(), container_of(), and list_for_each() are defined differently in several places throughout the kernel, so we can't just write one AST matcher to match them and map them to their arguments for the kernel_visitor to have access to.

Currently we don't implement any analyses for these macros anyway though, so figuring out how to lower them to MLIR without PASTA is not urgent. Worst-case scenario, we make another dialect/visitor for these macros and make PASTA a dependency for it.