[llvm] [mlir] Introduce a "log level" support for DEBUG_TYPE (PR #150855)

[Jacques Pienaar via llvm-commits]

https://github.com/jpienaar approved this pull request.

Overall looks good. In another lib there was 0 == always log, 1 == log if enabled, so here it _could_ have been to enable even if debug type is not set (e.g., if 0 then just emit rather than checking if debugging enabled). That was rather convenient during debugging (especially for cases where the pass is so deeply nested that plumbing flag through is tricky) where if needed, I could set all to 0 in the file.

https://github.com/llvm/llvm-project/pull/150855