No, it is not equivalent.
* `make clean` removes any build-related files (assuming that the
`clean` target is properly written). To see exactly what it would do,
run `make clean -n`. Judging from your question, I think this is what
you want to do.
* `git clean -xdf` would remove any files that git does not track. This
also includes build-related files, but also any other files that happen
to be in your working directory. For example, any output from `git
format-patch` would be removed by this, but not `make clean`.